Customizable Bridge test

This is a remix of Walters:
- http://www.thingiverse.com/thing:476845 (thanks)

**This version:**
- Forces the shape to be a half round.
- Adds a long bridge at right angles to the longest bridge.

This tests whether your cooling fan works as well at right angles when making long bridges.
It also allows you to test at maximum width of your print bed.