Added SimioPsychtoolbox class and will begin incorporating mix-in
Correcting lack of inheritance of SimioPsychtoolbox class in classdef of SimioEnv
SimioPsychtoolbox inherits handle, so it may be inherited by SimioEnv. Screen and PTB related properties relocated into SimioPsychtoolbox class
Removed redundant properties from SimioEnv
Continued adjustment to class structure for SimioEnv, with all drawing related functions moved into SimioPsychtoolbox. Created new wrapper method within SimioPsychtoolbox that uses a string argument to specify drawing type (texture, rect, etc.).