[localevaluation.elliptic] updated order() computation
[localevaluation.elliptic] prepare for specialization
[localevaluation.elliptic]
* added first draft of a specialization with diffusion factor and diffusion
  tensor to playground
[operators.elliptic-cg] removed config.h include
[operators.elliptic-cg] prepared for specialization
[operators.elliptic-cg]
* added specialization for diffusion factor and diffusion tensor to
  playground