Implement new and improved formatting input

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

...main/java/de/kuschku/quasseldroid/ui/chat/input/Editor.kt

...va/de/kuschku/quasseldroid/ui/chat/input/FormatHandler.kt

...ava/de/kuschku/quasseldroid/util/helper/IntRangeHelper.kt

...va/de/kuschku/quasseldroid/util/helper/SelectionHelper.kt

...e/kuschku/quasseldroid/util/ui/EditTextSelectionChange.kt

app/src/main/res/drawable-de/ic_format_bold.xml

app/src/main/res/drawable-de/ic_format_italic.xml

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

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

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

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

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

...ain/java/de/kuschku/libquassel/util/helpers/MathHelper.kt