[#30373] Which part to snap in volume snapping is removed

By Bug reported by Pep Ribal

Also fixed an object mode bug with volume snapping and made it compatible with the edit mode "Snap on self" option

[#30197] Snapping: Align rotation button

Reported by Pep Ribal

Volume snapping was showing invalid options.

[#29144] Snapping control points: can't choose which one to delete
Reported by Pep Ribal
You can now select which snap point to remove (with Alt-A) by moving the cursor over them.
Display colors are also used to indicate which snap points are active, selected or just there.

[#29611] Crash when scale one vertex with snap.
Reported by Andrey Penyaz
Scale snap defaults to 1 when snapping is impossible (distance to center of transformation is zero).

[#28801] Pet doesn't work on the whole mesh
Reported by Enrico Valenza

Mirror messes up the zone of influence. Disable mirror internally when proportional edit is on.

[#28681] Switching transform type doesn't register correct operator for 'repeat'.
Reported by Nicholas Rishel

Part of a potential fix, see discussion in tracker.

Snapping/Project

Disable editmesh as target if proportional edit is on (that was messed up incorrectly in revision 33233)

[#25886] Skeleton Sketching - Unclear UI for converting sketches into bones

Thanks Ronan Ducluzeau for the fix and Jason van Gumster for the report.

Fix register method order. Was broken when Campbell moved it to the C implementation.

register has to be called AFTER the type is registered while unregister has to be called BEFORE it's unregistered.

[#26622] Blender crashes when calling transform operator

Add cancellation checks for time* transforms that only run in specific spaces.

Hide Transform Mode operator property (it shouldn't be modified after the operator is run), made default mode Translate, not the useless Dummy.