Now uses the same as in the deck editor

Also, extracted the 2 new strings

+ Can be used for setting client size and closing the client.

Will expand on by sending client alerts to the tray.

Updated to push message notifactions to the toolbar

Preview image:

Added setting to enable/disable message popups

Added functionality

+ updated popup message and translation
+ Double clicking tray icon will now bring up the app/minimize it
+ can now be alerted of mentions
+ added setting to set if you want mentions on desktop
+ clicking mention message will take you to the main chat
+ added translations for icon menu
+ removed maximize/minimize/restore from menu, not needed.

Added disconnect

+ Disconnects any previous message slots/signals from the system icon
message bubble

This reverts commit 4568adb4.

 * ignore .tx folder
 * cmake: when UPDATE_TRANSLATIONS=ON, extract new strings only to the
english translation file.
 * added info in CONTRIBUTING.md
 * updated english translations

Translations have been updated.