Fixed filter for non-printable characters
Detecting more keys from Unity events
Handling tab key (control character)
Fixed handling of command sequences

Command sequences are Ctrl+C and Ctrl+Shift+X. They should be triggered
when pressing the 'C' or 'X' key and their handling should thus be done
before generic printable characters.  We use the information on the
currently pressed modifiers conatined in the Event structure.
Minor: more readable switch in Keydown()
Merge remote-tracking branch 'qsantos/guievents' into develop