Assets

[MatthewChrobak]

Asset management, in its current state, doesn't offer a lot of leverage for extensibility or customization.

• [x] Asset managers should be their own services, and not be owned by the services that use them
• [x] Textures asset manager should GC textures when not used after a period of time
• [x] pakfile assets vs raw asset managers
• [x] encryption/decryption
• [x] Asset managers should be responsible for CopyAssetsToBinary
• [x] Remove GetAssetManagers from IService