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
This patch puts the Symmetrize controls in the Symmetry panel. Not really sure where to put the Optimize button - here it's in Dyntopo still but we could move it elsewhere.