* picomodel: do some guessings about shader paths to handle more cases out of the...

* picomodel: do some guessings about shader paths to handle more cases out of the box; ones are based on material and diffuse map names:
		name w/o path: assume textures are in the folder, where model file is
		absolute path or with ..: try to cut at "/models/" or "/textures/" (as if leading to game folders); do previous case, if not
		strip extensions and turn slashes to forward ones anytime
	* picomodel::obj: fix diffuse map paths loading from .mtl