Spherical panoramic head - remixed

This is a remix of the panoramic head by BlacklightShaman. It is a very nice design - I especially like the quick release mount. I added a few mods to make it easier to use with my setup. These are as follows:

Horizontal arm:

- added alignment marks around the pivot point at 30 degree intervals
- made a cavity in the bolt area to accept/capture a nut for a 1/4" dia. x 20 bolt
- made a hole under the bubble level cavity so you can use a thin rod or drill bit to push the bubble level ba