Add top and bottom facet integration for zero forms.
Remove iteration set flags and add iteration descriptors.
Add the iteration descriptor to the loop cache key.
Add support for iteration over the interior facets by limiting the number of layers.
Stage in map for second vertical cell using current cell map and offset.
Attempt to add support for interior vertical facets.
Fix top facet maps in wrapper to include the size of the offset.
Temporary fix to counter the UFL integrals order mistmatch.
Add iterate enums to op2.