in_view_3d utility added
Revert "in_view_3d utility added"

This reverts commit 63158eef202f8320db738995b83ae256bc308e49.
Add nice themification!

This greatly simplifies the color assignment for the various elements, including the removal of the individual
them color options. The color preferences have been replaced with a simple Theme selector, just like Polystrips. Available themes are Blue, Green, and Orange.
Remove old Polystrips code.

Polystrips is now released as it's own add-on and so this code is no longer needed. Much of it (maybe all?) was outdated anyhow.
Merge branch 'refactor/remove-polysketch' into dev