New functionality to provide grid info in nested yaml sections

Providing grid info via nested yaml sections is now implemented. I.e. a section of the form

GRID:
  DOM1:
    TYPE: G
    R: 2
    B: 4
    GRID_NUMBER: 12
    EXTPAR_DATE: 20131001
    BASENAME:
      IFS: 'uc1_ei_t255_nc_remap_rev832'
  RADGRID: False

is sufficient to obtain correct grid, extpar and input data (if using official grids or using the same nomenclature) and linking this properly. This only works when parsing the namelist from a yaml file.

Linking of grid, extpar and input files in prepare_member.sh is now moved into a function.

Some further bugfixes and changes in behavior are documented in the changelog.

Closes #9 (closed), #25 (closed).