Overhaul of form generator

The MR changes the way generate_all_hyteg_forms.py behaves.

Selection of forms to generate is now based on the --filter and --geometry arguments in the following way:

• if neither --geometry, nor --filter is given, we generate all defined forms
• if only --filter is given, all forms matching the filter expression are generated
• if only --geometry is given, all forms that support the given geometric element type are generated
• if both --filter and --geometry are given, the intersection of both sets is generated

For this to work each FormInfo object now carries information which geometric element type(s) it supports.