Support loading custom pipelines/renderpasses

[brandonpollack23]

In order to support multiple pipelines, DrawableObject should contain a vec/array of textures (and uniforms) for each Descriptor. Nones are acceptable and replaced with the null texture.

The ordering is shader dependent on these textures, but this is why there are descriptor sets and layouts, recommend a user stick close to what the default is and try to do a good job :D

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#3