Dictionary in and dictionary out nodes

Created by: Durman

Addressed problem description

#2766 (closed)

Todo:

• Take default name of key from linked socket.
• Keep links of dictionary out nodes when a key of a dictionary was renamed. Next time or probably it even does not worth complicate too much. Simplest solutions was adding custom attribute for dictionaries.
• Robustness of determining type of output sockets. Next time. Simplest solutions was adding custom attribute for dictionaries.
• Consider handling of several dictionaries in list (ignoring mismatched keys?).
• Сustom draw for all sockets.
• Is_linked should have name was_linked before start of update event, more correct test is socket.links but as I suppose more expensive as well. Looks like in sv_get method is_linked should be replaced by links.
• deepcopy = False where it possible Deep copy is not implemented for dictionaries. In next PR.
• New dictionary icons 😄

Preflight checklist

• Code changes complete.
• Code documentation complete.
• Documentation for users complete.
• Manual testing done.
• Ready for merge.