Redo mouse/keyboard logic

[stefanhendriks]

(originally: Holding CTRL and pressing somewhere for rally-point simply no longer works.)

Changes for #290 broke setting rally-point behavior. While trying to fix that it became obvious that event-driven vs 'everything in one big mess' driven bite each other. In other words, it is best to redo this using the event-driven way.

TODO

• select structure
• select structure while having a group of units selected
• deselect structure (won't do)
• select / deselect unit (single click)
• select multiple units (box-selecting) from "normal" mouse state
• select multiple units (box-selecting) from "units already selected" mouse state
• repair state
  • repair unit (press R to switch to that state, press R again, or right-mouse click to leave Repair state)
  • repair structure
• add units to selection when holding SHIFT
• place structure (mouse state)
• deploy super weapon (mouse state) (deferred to Redo "Select target" mouse/keyboard logic #399)
• force attack (hold key: CTRL)
• force move (?)
• set rally-point (with right-mouse button instead of CTRL-click)
• react to keypress (key observer, like mouse)?
  • create groups (CTRL-1/5)
  • add to group (hold SHIFT)
  • select units by group nr
  • (required: report all keys pressed, or held for event, so that we can know if CTRL-1 is pressed for instance))