Map Object Tile resizing and object group resizing.

Quick summary of what's here:
- Object tiles respect the size parameters (set in pixels) and can be resized.
- Object tiles are initialized to the tileset image size on creation, and default to it on load.
- Moved ResizeHandle from MapObjectItem to ObjectSelectionTool, support group object resizing.

Caveats:
- Only supports the orthographic renderer. Isometric does not support object tile scaling correctly due to lack of boundingRect calculations.
- Still no ability to resize polygon and polyline objects.
- Object tiles have their size in pixels whereas most objects are in tile dimensions.
- Having to manually deal with tile offset on scaled objects is ugly.
- Scaling does not respect current object rotation. eg X axis movement always scales width.
- Negative scaling factors are not supported.