Option freeze layout ignored in standalone mode

[ciandonovan]

The option for freezing layouts was discussed and implemented in issue #21

However, it is not applied when running with the --standalone option.

While difficult due to the small click target, it is still possible to move and resize the widget in standalone mode by grabbing the top or sides of the window. There's no option then to restore the layout when running rqt -ht -t -l -f --standalone plugin without restarting the application. This is very problematic for "kiosk" or other embedded applications.

The --freeze-layout and --lock-perspective arguments are ignored if --standalone is set in qt_gui/src/qt_gui/main.py. It seems that this would be trivial to fix, however there could be reasons for this exclusion that I'm not aware of. If not, I'd be happy to submit a pull request on this issue.