Implement notification settings, fixes #48

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

...u/quasseldroid/service/QuasseldroidNotificationManager.kt

.../de/kuschku/quasseldroid/settings/NotificationSettings.kt

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

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

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

...va/de/kuschku/quasseldroid/ui/chat/topic/TopicActivity.kt

...hku/quasseldroid/ui/clientsettings/about/AboutActivity.kt

...ldroid/ui/clientsettings/client/ClientSettingsActivity.kt

...ldroid/ui/clientsettings/client/ClientSettingsFragment.kt

...hku/quasseldroid/ui/clientsettings/crash/CrashActivity.kt

...quasseldroid/ui/clientsettings/license/LicenseActivity.kt

...seldroid/ui/clientsettings/whitelist/WhitelistActivity.kt

...chku/quasseldroid/ui/coresettings/CoreSettingsActivity.kt

...asseldroid/ui/coresettings/aliasitem/AliasItemActivity.kt

...asseldroid/ui/coresettings/aliaslist/AliasListActivity.kt

...ldroid/ui/coresettings/chatlist/ChatlistCreateActivity.kt

...seldroid/ui/coresettings/chatlist/ChatlistEditActivity.kt

...id/ui/coresettings/highlightlist/HighlightListActivity.kt

...id/ui/coresettings/highlightrule/HighlightRuleActivity.kt