add HSP support

[poontology]

Adds support for storing and fetching Heresphere HSP files.

To test:

• play a video and seek to some position in Heresphere, open Video Settings, change Orientation sliders, click Orientation key-icon to add a keyframe to the current position, click save-icon at the top, prompt should show the server address, clicking Export should create the .hsp file on the server.
• to reload the API response switch to another video and come back to the previous video, mess with the Orientation again if you like, click download-icon next to save-icon, it should ask if you want to overwrite local settings from the server (for videos that don't have a HSP URL in the API response it'll say something about the local HSP file missing), click Import, click Orientation key-icon, the timestamps should be the ones stored on the server.

(In case anyone wants to run these features before they're merged without compiling their own there's release builds in my GH fork and a build in Docker Hub, just change docker-compose.yml to point to image: poontology/stash-vr)

[poontology]

There is a service called https://timestamp.trade/ that in addition to scene markers hosts HSP configs for the scenes, I wrote this script that queries all the local scenes that have markers (that might've been synced from the service) and attempts to export HSP from the service in to files. I found out however that at least for the moment the number of scenes with included HSP data is fairly low so it might not be so useful. Sometime in future it could be nice if the timestamp.trade stash plugin would itself write the HSP files into a given directory while doing a marker synchronizing run so there was no need to fetch them separately.

sync-hsp.sh