REQ: Loop Selection

[Niobium]

Uploaded version 1.1 to springdownloader.

Changelog:
- Uses the ground rather than the screen
- Works with moving camera
- Connecting line added for clarity
- Loop fades out after release

Also, you only have to be holding meta when you first click, you can release it after/while you are dragging, which makes it easier to move camera (I honestly don't know how you would easily move the camera and be selecting units, even if you didn't have to press a single key)

Unsure how to make it default, need some way for the widget to be the last on the list of things to check for handling mouse clicks, after the spring GUI and other widgets.