This reorganizes the cloth UI, and changes some of the behaviour to be more reasonable.

These are the changes included here:

• Reorganized cloth panels
• Improved some tooltips
• Removed vel_damping option (this had an unphysical implementation and added nothing that can't already be done with air_damping)
• Removed cloth pinning checkbox in favour of enabling pinning whenever a vertex group is selected for pinning (saves a redundant action)
• Removed stiffness scaling checkbox in favour of enabling scaling whenever a vertex group is selected for scaling (saves a redundant action)
• Separated shrinking from sewing, enabling the shrinking option to be used even when sewing is disabled (they are unrelated concepts and shouldn't depend on each other)
• Separated self collisions from object collisions, allowing their independent use. This avoids computing object collisions when only self collisions are desired.

Here is a side by side visual comparison of the changes (new version on the right):

Versioning could be added to this patch, for example to clear the pinning vertex group when opening an old file where pinning is unchecked, as well as other changes to keep the original behaviour, in parts where some flags have been removed. The question is if it would be more desirable to keep behaviour consistency, or logical consistency. For instance, with the pinning example, one might lose the group they had set in an old file.