Removes all programatic calls that modify the layout and uses the XML
resource instead.

This also introduces constants for the GROUP_ID, FORUM_NAME and
MIN_TIMESTAMP as they were used for the two buttons.

Closes #313

* If the user has already declined, we don't show that the other
  introducee has declined as well. The backend doesn't have that information, so
  this is compatible with the principle of showing what we know.
* If the user has already accepted or hasn't yet responded, we show the
  decline response in the private conversation with the introducer. If
  the user hasn't yet responded, we hide the accept/decline buttons
  in the introduction request message.

Messages an introducee receives in a `FINISHED` state are now being
ignored and deleted.

Closes #295

Will currently fail at runtime; requires a public key and a server onion.

* force decline when two of our own identities are introduced to each
  other
* throw away introduction requests to the same identity
  (impossible to trigger from UI)

Closes #284

(except refactoring of conversation item classes)

When devices' clocks are out of sync, it is possible that a response is
shown before the request. This commit makes sure that the timestamp of
responses is always later than the last message in the conversation.

Some wording could be misunderstood to thing introductions were
successful even though they were not. That has been clarified.

A new database transaction was created when getting contacts and local
transport properties. This has been changed to re-use the existing
transaction.

Also addresses minor issues found in review.

Show system notification for successful introductions

@color/briar_text_primary is used in a lot of places other than the settings screen - if we want to use grey text in the settings screen we'll need to find another way.

Also fixed some misspelled resource names and included the colours from the Briar palette in color.xml.

Includes code from https://github.com/consp1racy/android-support-preference
License: Apache License v2.0

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

Closes #211

This closes #204

* 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'

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

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.

and indicate which transports are currently available.
The icons have been chosen from the official material icons and might be
replaced later with icons that better represent the given transport.

Please note that I used vector drawables which will be automatically
converted at build time to raster graphics.

Closes #96

Provides a checkbox in the settings view, as well as an event handler to
disable/enable the tor network if the device is not on using the wifi
connection.

Refactors network-enabling code to a separate function. This function
is ran after the network state changes, or the settings change and
will update the status accordingly.

and fix message divider background for lower API levels.