EIQGEN feature enhancements 2

[istvanrath]

• annotation-style extension registry for eiqgen parameter contributions
• reorder import content assists to prefer epackages referenced in the eiqgen genmodels at the top
• preference setting to be able to change the name of generator.eiqgen

[ujhelyiz]

Migrated to https://bugs.eclipse.org/bugs/show_bug.cgi?id=398796