Improve first run experience & admin interface

[juliusknorr]

When enabling the app currently the background job will attempt to download the models and not really gives the admin or user feedback on the progress. It would be nice to have some indication in the admin panel about the current state:

• Waiting for the next background job
• Downloading models (show if successful/or failed)
• Maybe also add some details about how many users have been processed or are in the backlog

[bonswouar]

Here are some related suggestions, I'll let you pick what you like ;)

• Time of the last execution with unrecognized files (and maybe duration of the scan?)
• Time of the last recognized file (and maybe a link? => in user panel though)
• Details about the number of recognized media per model (ie number of landmark pictures, face pictures / different persons, etc) => could be per user also maybe?
• More precise handling of status (for example for video recognition, if you had an error at some point and then run the command manually, it will stay on " An error occurred during video recognition, please check the Nextcloud logs." while the command hasn't ended, even if some videos are recognized meanwhile)