Places the simple style editor in a frame with an Apply button.

This commit introduce a new dialog in SIF and the associated method in
UIFactory. It provides a way to build a dialog with an OK, an Apply and
a Cancel buttons. The dialog contains a single UIPanel. The Apply
behaviour is controled through an ActionListener.

I've intentionnally chosen not to use this panel for the advanced style editor. I've started working on a new advanced editor and I don't want to do the work twice. Moreover, the current advanced style editor already has a Apply button.