Support for assembling and editing frames via interactive viewport UI

[PsyCommando]

Tasks:

• Draw frame assembly viewport
• Display frame parts list
• Allow editing of individual parts and changing the image they refer to.
• Allow to add/duplicate/remove parts.
• Allow to move parts
• Fix viewport, parts list, and quick edit controls not synching properly!
• Select parts being moved/selected in the viewport in the parts list too!
• Allow parts multi-select
• Add snap to grid option
• Add snap to part option
• Document the viewport UI
• Add toggle for Y axis wrap-around.
• Allow displaying another existing frame onion skin style to help align things together!
• Frame auto-import tool.