Add basic EM endpoints

[gfrn]

As part of the effort to match legacy functionalities in full, EM endpoints (at least basic ones) should be added, alongside relevant testing. At the moment, I am focusing on implementing:

• FFT thumbnails
• Micrograph snapshots
• Movie data

Movies generally have some CTF/Motion correction data that is linked to them, more often than not in a 1:1 relationship, therefore I believe grouping and ordering them in one query could be sensible, as it makes pagination much easier in UI.

PS.: I have no permission to assign this issue to myself, add tags or create a branch, so the PR will have to be made from a fork