Partially reorganize assets layout and clean up
Models are now placed under Assets/Models
Textures are now placed under Assets/Textures
Materials are now placed under Assets/Materials
Some of the names of assets are changed
Some useless files are removed
Known issuses:
Some models cannot setup proper link to materials in Unity,
such as the magical circle door

Some models have not been scaled and rotated correctly
because these operations may break existing animation