Allow highlighting of own messages

.../java/de/kuschku/quasseldroid/settings/MessageSettings.kt

...rc/main/java/de/kuschku/quasseldroid/settings/Settings.kt

...e/kuschku/quasseldroid/ui/chat/messages/DisplayMessage.kt

...e/kuschku/quasseldroid/ui/chat/messages/MessageAdapter.kt

.../kuschku/quasseldroid/ui/chat/messages/MessageRenderer.kt

...u/quasseldroid/ui/chat/messages/QuasselMessageRenderer.kt

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

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

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

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

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

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

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

app/src/main/res/xml/preferences.xml