Prepare for buffer join/create UI

.idea/copyright/Quasseldroid.xml

.idea/copyright/profiles_settings.xml

app/build.gradle.kts

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

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

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

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

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

gradle.properties