ProjectionEditor: show code label aliases
fix broken logic for changing a relation to abstraction
codeOrLabelAt -> codeOrPathAt
codeOrPathAt: remove refacturd
renderRelation: show aliases in projection

other:
-subRelation:
  -clarify definition
  -return nothing() instead of throwing exception
   when relation is a projection or target is a path
-enable selecting a projection within RelationField
-update .gitignore
-rename "event" interface methods to present tense
add menu to select projection by navigating through code tree

-ChoosePatternMenu -> PatternMenu
-LabelSelectMenu -> LabelMenu