Menu: improve activity search

• It feels better to see a cursor while typing also on Android. Therfore always give the textfield focus and force hide()ing the native inputMethod when GCompris' VirtualKeyboard is used. There seems to be no other way to prevent the OS' keyboard from popping up.

When using the OS keyboard (i.e. virtual keyboard is deactivated in
config):

• Fix updating the search result onTextChanged by setting the ImhNoPredictiveText hint.

• Don't start the first found activity onEditingFinished ('Return'), just hide the keyboard, to let the user select his activity.