Also removed unnecessary adapter notifications in various places.

Whether or not a class needs to run as a service is an implementation decision.

also run setting the default preferences in a background thread

Closes #184

Due to the nature of how Android app install/uninstall works without
root, this requires manual confirmation after a panic was triggered.

Closes #211

* Only show them as unread when they arrive out of order
* Mark all messages as read when sending a message

The method `runOnDbThread()` depends on an executor
that's created by roboguice at startup.
It requires to be signed in, so use a different thread instead.

PanicKit does distinguish between two kinds of panic responses:

* default responses such as logging out which are non-destructive and
  do not require user interaction, so that the basics work without
  configuration
* destructive responses such as deleting user data. These require
  some sort of authentication to make sure they are not triggered
  by malicious apps

The second type of responses is implemented with this commit.

Authentication is done by comparing the package name
which is very weak. It requires the user to opt-in to
destructive responses and to configure from which app
to receive those (since there might be many different panic
trigger apps).

While possible to uninstall an app and install one with the same
package name afterwards, this always triggers notifications to
the user (if the attacker does not have root access).

Still that is no sufficient security for Briar's requirements,
so that TrustedIntents are used as well to make sure that the
app sending the destructive trigger is signed by a signing key
that we specified before. Currently, that is the one from the
GuardianProject and from IilabEngineering who does the Amnesty
International Panic App.

The responsibility of checking that the panic TRIGGER is
legitimate lies with the app responding to the trigger, so Briar
in this case. This commit checks whether the TRIGGER comes from
a trusted app before performing destructive actions,
but does perform the default action even when triggered from
untrusted apps.

Closes #210

This closes #204

Also removed some unused code from BaseActivity.

* removing screen border visible on small screens
* showing noticeable error message on wrong password input
* showing keyboard again after entering wrong password
* making lost password link easier to recognize as link
* renaming keyboard toggle method from 'hide' to 'toggle'

This is done by update existing items rather than just adding them,
because different timestamps in added items change the sorting criteria
and cause duplicates in the SortedList.

Closes #200

This now handles progress bar and empty view itself.
With this commit, it also scrolls down on layout changes like when
keyboard is opened.

Also fixed some IME action issues on Android 2.3.

It is a common pattern to have a list with an empty view and a progress bar.
This commit introduces a custom BriarRecyclerView and uses it for the
contact list.

No more manually hiding and showing empty views and progress bars is
necessary when using the new BriarRecyclerView instead of RecyclerView.

Please note that this conflicts with !44 at the moment and needs to be
implemented for !36 once merged.

Closes #198

The button hides itself when you scroll down the list of contacts
and shows again when you scroll up.

To properly color the button, the accent color has been defined.
It uses the same color as the action bar (primary color).
I leave it to a UX designer to adapt the color scheme.

Please note that the design support library was used.
It includes the app-compat library, so this has been removed
from the `build.gradle` file.

Closes #199

This addresses part of #197

properly notify the view adapter of dataset changes
in order to avoid invalidating the entire dataset when not absolutely necessary.

This change also shows unread messages in a different color,
so users do not fail to notice delayed messages.

It now uses conversation bubbles in alternating colors
and vector drawables to indicate message state.

The conversation bubbles have been taken from Telegram
and can be replaced by a UX designer later.

This commit also addresses #9, because message text can
now be selected and copied. This is done by using

    android:textIsSelectable="true"

which only works for API level 11 or higher.

If we want copy and paste on lower API levels,
additional measures have to be implemented.

When you receive a message from a contact,
it will be moved to the top of the list with a nice animation.
Also with this commit, not the entire data set is invalidated each time data changes,
but only the parts of the data that really require an update.

Furthermore, the ContactListItemComparator that is not needed anymore is
removed.