[UIFe] Improved Multi-monitor support for Unity2D

[Gerry Boland]

Hello list!

To keep feature-parity with Unity, Unity2D has to make some UI changes
regarding Multi-Monitor support.

There are no string changes, this is purely a notification.

Key aspects of these changes include:
- launcher available on every screen, or just one screen (configuration
option still required in System Settings however)
- dash/hud appear on screen containing mouse when summoned
- launcher arrows/pips reflect if windows are on current monitor/other
monitor
- summon launcher using mouse by pushing against screen edge

Please find more details in the bug report:
https://bugs.launchpad.net/unity-2d/+bug/954175

Please let me know if this is problematic, else I'll request the UIFe
from the release team.
Many thanks
-Gerry