- Q shall only contain forward model variables. And match ARTS as
closely as possible.
  
   - No covariance definitions in Q.


- Use notation grid1, grid2 and grid3 for retrieval definitions. 

   - This both in Q and for definition of covariances.
   - To allow general Atmlab functions


- The control file is created for each run. 

   - This allows to use the variable2file functionality in qarts2file.
   - As many variables as possible are stored to files in arts_oem_init.


- Definition of Jacobian a large structure

   - Following Q.CLOUDBOX/SENSOR/BATCH.
   - Main field names follows corresponding jacobianAdd method 
   - Each retrieval quantity has a DO field (where all can be 0).
   - Solution for ABS_SPECIES:
       J.ABS_SPECIES(1).DO       = 1;
       J.ABS_SPECIES(1).METHOD   = 'analytical';
       J.ABS_SPECIES(1).UNIT     = 'vmr';
       J.ABS_SPECIES(1).P_GRID   = z2p_simple( 0e3:1e3:90e3 );