Pipeline: Create PDF when HTML report is created

[rhodges]

If a user chooses to download a .PDF report, there is currently a long wait for the file to be created.

• Ensure this is still the case, especially after new logic is created to generate more printable map images (Render (all?) maps with MatPlotLib #421 )

We can speed this up by triggering the creation the .PDFs when the report is loaded.

• On report load, check if the .PDF exists or is currently being created ('running')
  • The report model should track:
    • Status of .PDF creation ('pending', 'running', 'complete')
    • Date of last attempt to create .PDF (to detect 'hung' processes)
• If file does not exist and status is not 'running' (or 'run date' is over 30 minutes old):
  • Ensure any required data (like map images) are created and ready
  • Create 'full report' .pdf
• Remove any logic that triggers .PDF creation when users click the full-report 'download' button
• Single-section reports (see Allow users to download individual sections of the report #425 ) should be snappy without pre-rendering since the images were all created for the 'full-report'