Feature: Single/Embedded YAML Document

This adds 2 major features to the YAML loading system:

1. All content can now be consolidated to a single YAML file. This is good for preparing for releases, as well as small games with little content.
2. The single YAML file can be embedded in the executable. This is done by adding `"versions": [ "ImportContent"]` to the `dub.json` file, and making sure to set `stringImportPaths` to the location of `Content.yml`. The advantage of this is that it means only art assets (textures and meshes) need to be distributed along side the game. This means that modding will become very difficult (unless purposefully left easy).

See the [`feature/SingleYamlDocument`](https://github.com/Circular-Studios/Sample-Dash-Game/compare/feature;SingleYamlDocument) branch in sample game for more info.