add platform interface for ORD combining tool

[vinulw]

Add a platform interface for running the ods_tools combine command line tool (OasisLMF/ODS_Tools#221).

Related to OasisLMF/ODS_OpenResultsData#3

[vinulw]

Initial endpoint structure outline:

analyses/combine/

• POST - create new combine job
• GET - get all the combine jobs info

analyses/combine/{id}/

• GET - get info of combine job specified by {id}
• DELETE - delete combine job {id}

analyses/combine/{id}/output_files/

• GET - get the output files from the combine job {id}