Add upload/import and download/export remote web admin ui or url endpoint for such

Currently if I want to save the json from a homehabit install I have to bring up the remote admin ui in browser and then select all copy and then paste into a local text file. Same but in reverse to restore. If the browser ui had had buttons for upload/import and download/export this process would be more streamlined.

In fact it might be great if I could just curl an api endpoint and get a copy of the json. In this was I could automate backups of the configuration