PBR-Material and StandardShader Improvements

[HugoPlacer]

• [ ] Revise the texture variable assigment in the Standard Shader because there are some weird things happening.
• [ ] Load Material Parameters from the assimp.
• [x] Adjust the Material Component Sliders.
• [x] Make a good Material Component UI.
• [ ] Some controls does not have so much sense.
• [ ] Fix a bug that causes the sponza to shine in wrong ways.
• [ ] Add some way to differentiate if the metallic and roughness textures are the same texture or different and if are the same texture what channel uses for each value. (the DamagedHelmet uses the single texture aproach, Sponza uses the single texture aproach but instead of using the red and green channel uses the green and blue channels.

[HugoPlacer]

It seams that assimp don't expose any material parameter for the PBR Material Pipeline. An alternative to this could be check if the material has the texture and set the needed value for the parameter (for example: for the Metallic if not has the texture metallic is 0 and if has the texture metallic is 1).

[HugoPlacer]

I do it and it seems to work :p 5e2475812cad033c4becce85972d4b24fce0d180