Unify presentation logic between SPICE and Terminal modes

[osy]

The purpose of this change is to make things more maintainable in the future by keeping common presentation logic shared by SPICE and Terminal in one place (rather than copy-pasting many parts).

• Refactor toolbar, keyboard accessory, blur background into separate NIB
• Common VMDisplayViewController super class shared by Metal and Terminal frontends
• Fix modifier keys on external keyboard (fixes Console mode: external keyboard modifier keys #285)
• Terminal become first responder on key press (13.4 only) (fixes Console mode: external keyboard requires software keyboard to be open #284)
• Fixes Console mode: top and bottom lines hidden #283 by using improved toolbar size from previous release
• Fixes Console mode: crash on pause #286 by using pause/resume logic from previous release