Show avatars in buffer list

...kuschku/quasseldroid/ui/chat/buffers/BufferListAdapter.kt

.../quasseldroid/ui/chat/buffers/BufferViewConfigFragment.kt

...de/kuschku/quasseldroid/ui/chat/nicks/NickListFragment.kt

app/src/main/res/drawable/ic_status_channel.xml

app/src/main/res/drawable/ic_status_channel_offline.xml

app/src/main/res/drawable/ic_status_offline.xml

app/src/main/res/layout/widget_buffer.xml

app/src/main/res/layout/widget_buffer_away.xml

app/src/main/res/values/dimens.xml

...ava/de/kuschku/quasseldroid/viewmodel/QuasselViewModel.kt

...ava/de/kuschku/quasseldroid/viewmodel/data/BufferProps.kt

...va/de/kuschku/quasseldroid/viewmodel/data/BufferStatus.kt