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.

Closes #179

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

UI was transferred into XML files
and lots of redundant code was deleted such as the custom CodeEntryView.

Closes #33

Users were confused by the process of adding a contact for the first time.
This change adds additional explanation and a picture of what is going on.

It also moves part of the UI into XML files.

Closes #87