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.
