Support manager-uploaded solutions (viewable in client)

Plom needs to be able to handle solutions.

• Manager needs to be able to upload/check/replace solutions (fixes #337 (closed))
• Client needs to be able to view solutions
• On return, students should be able to get their personalised solutions (for their particular versions of questions)

To do this

• work out why it keeps failing CI runs - help @cbm755
• plom-solution script to upload/download/status-check solutions - single image for now
• auto-extract pages from solution pdf (assuming same pages as test) and turn into images for upload
• also give option of a solution spec.
• server has get/put/status API
• plom-solution script can delete a solution (in case of idiocy)
• decide where to store the soln on the server
• server has API for marker-client to get soln - maybe migrate the one currently used by soln-script.
• client can get solution and display it (and can refresh it)
• manager-ap can get/put solutions (don't need to use the script)
• plom-demo and plom-hwdemo build solutions
• plom-demo and plom-hwdemo upload solutions
• as part of test-reassembly, optional solution assembly
• optional "click here to get your soln" as well as "click here to get your marked test" on the automagical webpage.
• decide if individualised soln need a cover page.
• decide if soln should be included in reassembled test instead of as separate pdf. - I decided - separate
• decide if solns on webpage need code as well as student number - Decided = just SID. If this opens some security whatsit then that can be a future MR.
• ci runs need to incorporate soln.
• dry up much of the reassembly code (soln, coverpages, etc)
• move soln spec parsing into specVerifier.
• cat photos
• de-excerementise the solnSpec toml
• changelog and other misc docs.