Complete implementation of exterior facet integral generation for ffc

[Martin Sandve Alnæs]

(Copied from launchpad, some of this is already in place.)

To enable rudimentary integration over exterior facets, uflacs needs to implement:

• Geometry mappings
• Quadrature rule
• Integration scaling factor
• Basis function value tables
• Basis function derivative value tables with geometry mapping
• Facet normal

Advanced features are left to other blueprints.

[Martin Sandve Alnæs]

Was already marked done in launchpad.