Retry imports without creating duplicate runs

Scripts that push test reports on a schedule can now retry safely: a file you already imported is recognized instead of being imported twice.

• Added duplicate detection to structured imports (OpenHTF, WATS, ATML, NI TestStand, STDF, ATDF), through the API and the dashboard. Importing the same file again returns its existing runs and creates nothing.
• Added an allow_duplicate option to import a file again on purpose, as new runs next to the existing ones. The dashboard asks first when it recognizes a file.
• Fixed OpenHTF records without a procedure in their metadata, which now import from the dashboard, and WATS WSJF files with unnamed measurements. The file picker now also offers XML, STDF and ATDF files.