Feature/add basis size test
Add some consistency checking for indices/size of bases.
As long as gridviewfunctionspacebasistest.cc is not modularized
(see #28) it's easiest to simply call checkBasis(basis)
from there.
Currently this fails because it reveals a bug in basis.size(mi)
for LangrangeDGBasis
and BSplineBasis
. There, it's not properly
implemented if mi
is an existing multi-index.