Add TODO message into Xflow Graph
Add cl context passing trough executer to CLProgram
Remove unnecessary code from CLProgram and add CL context
Add a reference to the WebCL API into Xflow cl wrapper
Add first working version of CLProgram (WIP)

* WebCL operators completely integrated with WebCL API. No WebCL or
WebCL API calls required outside of Xflow architecture.
* Kernel code generator automatically adapts to Xflow operator
inputs/output parameters.
* Only main logical part of kernel code are required in the WebCL
operator.
  * This limits some of the processing possibilities provided by WebCL,
but reduces potentially unsafe/crashing operations and makes defining
Xflow WebCL operators easier.
* Note: This implementation works currently only with one 'texture'
type input and one 'texture' output.