Hide avatar and nick if the same user is sending consecutive messages

...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/layout/widget_chatmessage_plain.xml

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

...va/de/kuschku/quasseldroid/persistence/QuasselDatabase.kt

...e/kuschku/quasseldroid/viewmodel/data/FormattedMessage.kt