Blender Git Loki

UI: Re-organize Sculpt Symmetrize controls

Currently the UI for Symmetrize is confusing, for a few reasons:

- It exists as a sub-panel to the Dyntopo panel, even though it doesn't require Dyntopo to work
- It is inside a panel called Remesh, which is confusing because we now have a different Remesh panel

Changes:

- Put the Symmetrize controls in the Symmetry panel
- Rename Optimize to Rebuild BVH and move to the Sculpt menu
- Change the poll function - apparently it doesn't require Dyntopo

Differential Revision: https://developer.blender.org/D6735

Reviewed by Pablo Dobarro