Add UUIDs for resources

[mrDIMAS]

Fyrox resource system uses file names as their id, which adds a lot of headache in the following situations:

1. References must be fixed when a resource is moved across file system - this is very problematic, because it requires scanning the entire assets directory and loading each asset to look for resource references. If such reference is found, then it must be changed and the resource must be written back.
2. It is impossible to substitute a resource with more efficient representation for shipping builds - devs usually work with "raw" resources (such as jpg/png for images, fbx for 3d models, and so on) and these formats aren't very good for final game builds. Such resources could be pre-processed for shipping build to have more engine-friendly representation. For example all images could be converted into a format that have all mip-maps generated, 3d models can be converted to simple vertex+index buffers and so on. If the resource system used UUIDs, then this issue simply wouldn't exist because a resource data (file) associated with the UUID can be replaced entirely.
3. There might be some other very specific cases so this list might be updated.

UUIDs can be added pretty easily, but this system requires adding special metadata files near each supported resource. This metadata file must contain the UUID and maybe some other information. The name of the file must be the same as the resource but with .meta extension.

The engine must automatically create such files for every supported resource when it starts. So the UUID of a resource will always be loaded from metadata file and will be stable.