Add “edit helpers” for properties list in level creator

[Wuzzy2]

I have a big suggestion to greatly improve the usability of the properties list by adding little “edit helpers” which simplify the entering of values, depending on the “data type”:

• [ ] Number-based values should get a spin box with a sane step size and maybe upper and lower bounds
• [ ] ImageName should have a little button to open up a dialog where you see a list widget of image names to which you can add and remove entries. The “add” button should open up the image browser. The extra complexity is required since this field allows a set of images.
• [ ] Keys which allow a small fixed number of values only (such as Rotatable) should have a drop-down list with all valid values (and the empty/default value).
• [ ] Generally, all input fields must make it impossible to enter invalid values, important to protect TBE against bad data or even crashes
• [ ] PivotPoint could make use of the same editor, but here you only need to place one point
• [ ] Polygons could get an extra button which opens up a polygon editor.

The polygon editor is a very complex and probably time-consuming addition but will also be very useful, since manually getting polygons right is a huge pain in the ass. The editor should work like this:

• Displays object in background, maybe with 50% transparency or so
• Also displays a bounding box
• 5 modes: add point, move point, delete point, add polygon, remove polygon
• Maybe a 6th mode: move polygon
• Any mouse click does the action of the active mode (i.e. add point)
• Drag-and-drop for the movement modes
• TBE should check the polygons automatically, but automatic adjustments are not required, this would go WAY too far. If there's a problem (i.e. convex polygons), the “OK” button is disabled, and a label displays the issues
• User should not be bothered about weird Box2D oddities:
  • If required, TBE silent adds pseudo-polygons with one point only at (0.0,-0.5), (0.0, 0.5), (0.5, 0,0) and (-0.5,0.0) (one for each edge) on saving, for resolving AABB oddities. It's a hack, if you have a better idea, let me know
  • On opening the polygons editor, all “polygons” with 2 or 1 points are automatically hidden before showing the points to the user, since those are used for ugly hacks =)
  • TBE automatically makes the polygon go counter-clockwise (if possible)

The PivotPoint editor would be similar to the polyon editor, but simpler. It has no modes, it also displays the object and a bounding box. To set the PivotPoint, the user clicks on a point on the area. The point will get highlighted and in two input fields the PivotPoint coordinates show up in spinboxes. Then there's a confirm and abort button, of course.