formalize ec_data substructure for dimensions and units as well, ready for...

formalize ec_data substructure for dimensions and units as well, ready for automated output of main .ec.data from .ec.ec_data:xxx.data

git-svn-id: https://spcsvn.epfl.ch/repos/TCV/gdat/trunk@11575 d63d8f72-b253-0410-a779-e742ad2e26cf