ENH: Changes in FontPropertyWidget and TextLocationWidget

FontPropertyWidget: Added opacity spinbox to control font opacity.
TextLocationWidget: Changed listening from the groupbox clicked()
signal to toggled() signal so that QtTesting tests can simply use
set_boolean command on the groupbox.

Change-Id: Ib7a45875e60d9f70f8a7d4e6f7318750c485e6a8
FIX: Fixed test using the new TextLocationWidget

QtTesting currently cannot record the event of activating a toolbutton to bring
up the associated popup menu. To work around this issue, just add a line before
the QtTesting recorded line to activate the toolbutton.

Change-Id: I14d17187755a9b0595b173e4fc50d8313dd45899