File loaders

[FacoBackup]

• [x] Loader facade
  • [x] Mesh
• [x] LoaderData object, containing information like path and if is a static resource or a file
• [x] Remove material resource type
• [x] ~Mesh loader supports all the file formats that assimp suports~
• [x] New abstract classes for ExternalResource and NativeResource, whereas ExternalResource has a field pointing to the loader data
• [ ] Import button on file browser, will only pass the file's absolute path
• [x] ~Mesh loader will parse the scene and create entities if necessary, will also load textures if those are included with the file~
  • [ ] Requires texture loader #46
  • [ ] Requires entity hierarchy implementation #45
• [x] Add initialization step to resources service for loading static data like shaders and meshes
• [x] Resource service should be able to parse and serialize data
• [x] Resource loader keeps a list of all the imported files, this should be serialized too