Closes #71. Sources for abstractions with no suggestions are not limited by sections.
Closes #72. Sources for abstractions in edit mode are not limited to sections.
Closes #73. "Delete group" should allow to remove only groups added by user
Merge branch 'master' into suggestion_source_ui_fixes
Merge pull request #74 from NUBIC/suggestion_source_ui_fixes

Suggestion source fixes, restricted removing abstraction group to user-added groups.