Feature/evaluate basis gradient with loopy 2

Second try to implement issue #22. We avoid problems with diagonal matrices in the following way:

1. The user can give the option 'diagonal-transformation-matrix' to the form compiler if he wants to reduce the loop.

2. It is now possible to set options during the form compilation. When a YaspGrid is created we automatically set the option 'diagonal-transformation-matrix'.

Usually it makes little sense to provide the information yourself. I just wanted to add the possiblility if someone has a axiparallel grid that cannot be a Yasp Grid (eg. due to non rectangular domain).

Closes issue #22.

See merge request !13