Improved drawing/editing of openings.

1. New dialog showing the opening properties where you now get a preview of the opening and the possibility to set side. (Note that if no element is selected the preview will just show a "sample view" since side and cast type is unknown)

2. Possibility to draw and add openings to a wall by selecting a wall at command start.

3. Jigs for drawing openings where you can go back to the properties dialog, specify justification and offset and if the opening is to be added to a wall you get dimension lines showing the location within the wall.