Node groups UI

Created by: Durman

Addressed problem description

#3319 (closed) In this PR I'm going to add Group node and all functionality responsible for drawing its user interface. Adding group nodes is too big functionality I would be able to add it in one PR.

Preflight checklist

• Add group menu
• Add separate trees for groups
• Handling sockets creation
• Add tree description
• Add group in and group out nodes into menu
• Opertaor for creating group from selected nodes
• Operator for ungrouping
• Add the check if selection can be converted into a group
• Take into account frames during grouping / ungrouping (rerouters ?)
• Add import error _
• Code changes complete.
• Code documentation complete.
• Manual testing done.
• Ready for merge.