Add custom input mode switch

Hard code Control+Space to switch the input method on/off independent of
IBus support. Also add a tray icon and an 'InputMode' property (for
GNOME Shell) to show the current mode.

ISSUE: https://github.com/lewtds/ibus-ringo/issues/10
Remove unneeded files and fix install script
Fix a wrong method name call
New debian build script
Bring test/test_engine.py up to date with the current code