Implement formatting editor

...n/java/de/kuschku/quasseldroid_ng/ui/chat/ChatActivity.kt

...in/java/de/kuschku/quasseldroid_ng/ui/chat/InputEditor.kt

...de/kuschku/quasseldroid_ng/util/helper/SelectionHelper.kt

.../quasseldroid_ng/util/irc/format/IrcFormatDeserializer.kt

...ku/quasseldroid_ng/util/irc/format/IrcFormatSerializer.kt

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

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

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

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

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

app/src/main/res/layout-sw720dp-land/activity_main.xml

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

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

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

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

app/src/main/res/menu/editor.xml

app/src/main/res/menu/input_panel.xml

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

...quassel/protocol/primitive/serializer/StringSerializer.kt