Integrate changes from Deimos

[benjaminchlee]

This pull request integrates (some of) the changes made to DxR during the development of Deimos.

New features:

• Marks, axis ticks and labels now use object pooling to improve performance during Vis updates
• Maps can now be created using spatial channel types and GeoJSON data (using GeoJSON.Net)
• A new RuntimeVisSpecsInspector has been added to improve usability of editing Vis's during runtime
• Added new example scene to demonstrate these features

Modifications to DxR:

• Updated to version 2020.3.44f1 due to severely out of date .NET API
• Removed HoloToolkit scripts due to being obsolete (this likely breaks interactions)
• Updated SimpleJSON package

[benjaminchlee]

I just noticed this has been sitting here for the past 5 months @ronellsicat

[ronellsicat]

Apologies. I have other more urgent projects at the moment. Will get back to this at some point. :)