Minor bugfixes and performance improvements

...ain/java/de/kuschku/quasseldroid/dagger/SettingsModule.kt

...in/java/de/kuschku/quasseldroid/service/QuasselService.kt

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

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

...main/java/de/kuschku/quasseldroid/ui/chat/ChatActivity.kt

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

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

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