Fix missing extended keycode and 'up' action when sending release key events. Fixes #7

When a remmina RDP window lose its focus, all pressed keys are removed
by sending a release event to the RDP server. This event was
missing the extended keycode and the 'up' action.
Merge pull request #328 from giox069/gtk3

Fix missing extended keycode and 'up' action when releasing all keys