Early implementation of notification handling

...uschku/quasseldroid/service/QuasselNotificationBackend.kt

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

...a/de/kuschku/quasseldroid/service/QuasselServiceModule.kt

.../quasseldroid/ui/chat/info/channel/ChannelInfoFragment.kt

...uschku/quasseldroid/ui/chat/info/user/UserInfoFragment.kt

...ava/de/kuschku/quasseldroid/ui/chat/input/EditorHelper.kt

...ava/de/kuschku/quasseldroid/ui/chat/input/RichEditText.kt

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

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

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

.../kuschku/quasseldroid/ui/chat/messages/MessageRenderer.kt

...u/quasseldroid/ui/chat/messages/QuasselMessageRenderer.kt

...rc/main/java/de/kuschku/quasseldroid/util/AvatarHelper.kt

.../java/de/kuschku/quasseldroid/util/NotificationMessage.kt

...chku/quasseldroid/util/QuasseldroidNotificationManager.kt

.../kuschku/quasseldroid/util/irc/format/ContentFormatter.kt

...hku/quasseldroid/util/irc/format/IrcFormatDeserializer.kt

...schku/quasseldroid/util/irc/format/IrcFormatSerializer.kt

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

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