Export of models as C++ code

[Yuri05]

Models exported in form of a C++ code can be compiled with a C++ compiler and used e.g. from R, Matlab, Android etc.
Simulation of compiled models is much faster (average factor 10-12) compared to simulation in PK-Sim/MoBi.

Export is based on an individual or population simulation. Depending on the type of the simulation, some parameters can be set as variable, which will allow their variation in the compiled model.

When exporting from an individual simulation: s. Issue (TODO) for details
Move this to a separate issue

* which parameters should be set as variable?
  * Option 1: None
  * Option 2: Favorites
  * Option 3: selectable by user (per default: all parameters from favorites could be selected)

When exporting from a population simulation: s. Issue (TODO) for details
Move this to a separate issue

Parameters varied in a population must be set as variable. Additionally, some other parameters can be set as varied
  * Option 1: None
  * Option 2: Favorites
  * Option 3: selectable by user (per default: all parameters from favorites could be selected)