Bugfix in "finitelement in sobolevspace" operator.
Just commenting and whitespace in cell.py.
Add bunch of tests of the type "V in H1".
Sketch part of implementation of change to reference value representation with piola mappings.
Sketch new PullbackOf operator class.
Add sobolev space to element list and fundamental (i.e. not
mixed etc.) elements. Some refactoring in the process, cleanup and
commenting in elementlist.py, moved some checks from
finiteelement.__init__ to a elementlist helper function,
such that the interpretation of the elementlist data is
contained in elementlist.py.
Fixes in designated spacesfor elements.
Import sobolev space objects in ufl namespace.
Add ipython notebook latex rendering of sobolevspace objects.
Improve svg rendering of cell in ipython notebook.
Add mapping to elementlist and store with FiniteElement.

Need to sort out how to handle these properties in mixed elements.
Attempt at optimizing Indexed.operands() which is called a lot by
creating the operands tuple in the constructor instead of storing
expression and indices as separate members.
Add comments for where to build enabled_coefficients list.
Build enabled_coefficients array for each IntegralData object.
Rename mappings from "affine" to "identity" in elementlist.
Bugfixes following change of internal members in Indexed type.

There's too much direct access of ._foo members around...
Bugfix: add back value_rank to elementlist because DRT is L2 so
value_rank cannot be determined by sobolov space.
Merge branch 'martinal/topic-add-sobolev-spaces-to-elementlist'
Merge branch 'martinal/topic-add-enabled-coefficients-per-integral'