Data Assets
This merge request adds Data Assets to the engine. Data Assets will cover the needs of most engine systems, as well as most of Socially Distant.
What you can do
You can now change the engine's render pipeline, since render pipelines are now data assets. You can do so in Project Settings:
I've also added a simple data asset editor to the engine. It's just an inspector.
Documentation
Documentation for both Render Pipelines and Data Assets in general can be found on the GitLab wiki.
Fixes
When opening an asset editor, the engine will now re-use the already-loaded asset if the asset you're trying to edit has been loaded elsewhere in the engine. This means that, when editing the project's default render pipeline, you'll see changes reflected in the main Scene View.
The InspectorDocumentPane now takes an IReadOnlySelection instead of an ISelection, and no longer expects inspection providers to implement IEditable. This makes the inspector API significantly less of a nightmare to deal with.

