Perform small updates in simplified metamodel

[Aurelien-Pin]

Perform several small updates in the simplified metamodel:

• rename method type on EObject to avoid conflict with attribute type of some elements
• update diagram export method to support different formats
• define containment relations as read-only (users will use create, move, delete but will not modify containment relation directly)
• define containment of categories and physical paths
• add shortcut to access system directly from the perspective
• check that relations can be navigated in both directions

[Aurelien-Pin]

Implemented in https://github.com/labs4capella/python4capella/commit/f6f7f9b7f0c0d2eecc05a4ec09007a01fd6444f6, https://github.com/labs4capella/python4capella/commit/e5518bfe00f3629a10e85711b149fcf5f9fef079 and https://github.com/labs4capella/python4capella/commit/da8c5f99a4796c0b6ce7ca10d286cd5ff220186d