shell: Follow Hawaii.Shell.Controls.Style changes
applets: Add notifications applet

As by Jens wireframes.
shell: Replace system tray with notifications applet

That should really be replaced by a system tray that follows our
user experience but that's not currently available.
shell: Define __control for panel style
shell: Use Hawaii buttons for control center panel
shell: Replace Plasma calendar with Hawaii's in control center
shell: Use Hawaii controls in widgets explorer