Expose preedit as property

Allows a dirty way to get access to current preediting state from
application side.

RevBy: Michael Hasselmann
Use Qt::Window flag for maliit windows

Unlike Qt documentation promises, it's currently possible to
unset Qt::Window even if no parent exists. But explicit set of
flags is better, so adding it.

RevBy: Michael Hasselmann
Avoid better sending events to null objects

Qml TextInput element was able to cause crash by having selection on
focus out. That (incorrectly) causes update() to trigger. Better
to be more careful on input context side.