Core: Make IEditor::id a value member and adjust users

Change-Id: I47e457c4a1821c515cd8a740d27bfe005a0c09e6
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Beautifier: edit UI text

Make error message wording more consistent. Fix some
punctuation and grammar issues.

Change-Id: I21298fea201ff51635d4b6fa9f57445bc94dd0db
Reviewed-by: Lorenz Haas <lykurg@gmail.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>