TMSS-183: reapplied reverted commits cad13a89 39f64d7f 9e39ce94 8e7b08e6 25d2e3f2 e4dbedc9 0015db7c c5ba3df4 6c9575c4 with JIRA issue number TMSS-183

TMSS-183: reverted commits cad13a89 39f64d7f 9e39ce94 8e7b08e6 25d2e3f2 e4dbedc9 0015db7c c5ba3df4 6c9575c4 because they had no JIRA issue number

TMSS-153: added little factory to pick the proper conversion method based on subtask spec template name

TMSS-153: and TMSS-145: fixed populate.populate_lofar_json_schemas according to https://support.astron.nl/confluence/display/TMSS/UC1+JSON
There are now two Task schema and 1 Subtask schema.
Used the schema's, added dataproducts, convert everything to parset.

TMSS-153: added most parset keys according to https://support.astron.nl/confluence/display/TMSS/UC1+JSON
still working on the quite complicated dataproducts