Add support for Snapshot, Difference and Temporal Grouping Operators

[ChrizZz110]

Add support for

• Snapshot operator
• Difference operator
• Grouping operator

This refactors the Gradoop Demo to the Temporal Graph Explorer

[tonnyhideyori]

Have they added Temporal graph in the demo already

[ChrizZz110]

@tonnyhideyori Sorry, is that a question? There is an ongoing work to add support for these three operators atm.