Refactor Far API.
* replace void* of all kernel applications with CONTEXT template parameter.
  It eliminates many static_casts from void* for both far and osd classes.
* move the big switch-cases of far default kernel launches out of Refine so
  that osd controllers can arbitrary mix default kernels and custom kernels.
* change FarKernelBatch::kernelType from enum to int, clients can add
  custom kernel types.
* remove a back-pointer to farmesh from subdivision table.
* untemplate all subdivision table classes and template their compute methods
  instead. Those methods take a typed vertex storage.
* remove an unused argument FarMesh from the constructor of subdivision
  table factories.