DIN rail Designer 0.81

0.81 bugfix removes the SMA fastener clip option, since this hasn't really been implemented yet.

0.8 update adds some features not yet documented. Seems to have broken Customizer as well. Sorry.

This "Designer" is for creating DIN rail holders. So far the features are:
* Creates a holder with a circular hole
* The size of the top and bottom can be independently customized
* Optional removal of mid-section to save material
* Optional finger-pull to release the clip
* A customized chamf