Improve and document extensibility of Cooperate

[seiferma]

We should provide a manual for including a new diagram into Cooperate. The manual shall be located in the Github wiki.

In order to allow extending Cooperate in an non-invasive way, we have to introduce extension points, remove not-extensible enumeration types, and streamline the bundle dependencies. #77 should be done before this issue.

Afterwards, we should restructure the update site to allow selecting/deselecting features based on diagram types.

[sdkrach]

Results from our architecture refactoring meeting

• Move CDOXtextEditor to d.c.m.t.xtext.runtime.ui bundle
• Extend transformation factory extension point with post processors
• Refactor New Diagram Wizards into separate plugins per Diagram, include documentation
• Unify Categories for PrefPages
• Split d.c.ui.focus.papyrus by diagrams
• Split d.c.ui.papyrus by diagrams
• Merge TextualCDOEditorID Enum with existing enums / type registry
• Remove dependency to ActiveMQ
  • At least from ConnectionUtils
  • Replace with custom Net4j signal
• Change name of CustomCDOMerger to sth sensible ("NilFixing...")
• CDO Helper in CDU Utils Util necessary? Inline functionality if only used from one position
• Create Class for CDO Connection Constants
• Document restrictions of ModelNamingConventions (only two diagrams)
• Unify namespace in d.c.m.graphical.papyrus.extension
• Split d.c.m.graphical.papyrus.extension by diagram types
  • also PapyrusViewpointCustomizationHelper
  • add extension point for custom customizers (maybe only rules necessary)
• Refactor constraints in d.c.m.graphical.papyrus.extension into separate bundles by diagram
• Fix UseCaseImportedNamespaceAwareLocalScopeProvider (unqualified import of use cases not working)
• Extrace magic strings into constants class

Optional

• Replace editor type enum with extensible registry