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 was outdated anyhow.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
Merge branch 'refactor/remove-polysketch' into release/1.2.0
Add polyfill for nicer face visualization.

This way the faces between loops now draw with 20% alpha of the current geometry theme color.

Note: I've added the draw_quads_from_3dpoints to the Contour Utilities, but this should really reference common_drawing. Will refactor later along with the rest of the codebase, such that all utilities are pulling from the common lib.
Merge branch 'interface/polyfill' into release/1.2.0
Merge branch 'interface/polyfill' into dev
Prettify all da things! Add point smoothing for nicer handles and vertices.

This makes the handles and vertices draw as nice, smooth circles rather than squares.
Add point smoothing to the cut lines.
Merge branch 'interface/nice-handles' into release/1.2.0