Asset system integration

[karnkaul]

Main should initialize and use the asset system for loading shaders (and eventually textures, fonts, etc).

[TymianekPL]

Sub-issues resolved; closing

[karnkaul]

The temp shader loading code in main needs to be replaced with loading a shader through AssetLoader for this issue to be closed

[TymianekPL]

I'll make a sub issue then