…perfluous release events

These events may be sent by the IM, and meant to reach the client.

check:

* in firefox, no text input, press ctrl-l, there should not be
  continuous l being inserted into the urlbar
* in firefox, with text input, press super+some key to switch workspace
  and back (but don't release super inbetween). click in firefox, super
  should not be consider pressed
* with text input, does the switcher plugin activate and deactivate correctly

IM sends release key events when deactivated, which caused e.g. the
switcher plugin to deactivate early. The plugin has a higher priority
when activating, but lower for subsequent key events.

fcitx5 no longer commit_string on deactivating.

Or we'll alternate between two keyboards, sending a lot of keymap and
repeat_info events to all clients.

…t method reconnects