Fixes

[amirgon]

• Incorporate https://github.com/olofk/ipyxact/pull/32
• Use globals() such that ipyxact could be used as a git submodule.
  Otherwise classes generated by _generate_classes are inaccessible from parse_tree when ipyxact is imported through another hierarchy (from ipyxact.ipyxact.ipyxact import Component)
• Add missing dim attribute to register element and mask attribute to reset element

[olofk]

Many thanks for this. Picked and pushed