Integrate theme settings into compilation

[oliverfoster]

Subject of the issue

AAT theme settings should come into compilation process as expected json properties.

core schema https://github.com/adaptlearning/adapt-contrib-core/blob/d1d4aae7bf2b2114629435a3136af7d571cf8a32/schema/config.schema.json#L401-L405

vanilla schema https://github.com/adaptlearning/adapt-contrib-vanilla/blob/e2260e8fb62a76a96bf5df9cf7d446bd15757f8c/schema/theme.schema.json#L2

Such that the properties and values are accessible in the config, less and css spaces.