Implement significantly faster DayChange headers

...kuschku/quasseldroid/ui/chat/input/AutoCompleteAdapter.kt

.../quasseldroid/ui/chat/messages/DayChangeItemDecoration.kt

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

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

...chku/quasseldroid/ui/chat/messages/MessageListFragment.kt

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

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

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

...kuschku/quasseldroid/persistence/QuasselBacklogStorage.kt

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