Blender Git Loki

Tweaks to bevel and crease transform

They were using INPUT_SPRING in a way which didn't allow
it to easily redo the operator because INPUT_SPRING internally
is stored as a ration between old value and new one and crease
and bevel were converting this to value delta.

Now made it special input type INPUT_SPRING_DELTA which is
storing delta of the spring, meaning now values in the redo
panel kind of makes sense -- they mean how much to add/remove
to the crease/bevel weight.

Expect to be no functional changes from interactive transform
POV, just a bit more convenient to use redo panel.