Remove the json action

Raw report json can now be obtained from the show action using
Accept: application/json header.
Allow partial import of reports

Before: if some of the reports sent in a request failed to import for
some reason, none were imported (and proxy deleted them all).

Now: all reports that can be imported can be imported, errors are
logged. If at least one report is imported successfully, proxy deletes
all of them.
Dashboard graph uses 1 db query, resolution 1 day