Adds functionality to export images on program close, it also deletes
the originals from the database and the content folder. It also deletes
the content folder itself. But before it does anything it asks the user
for confirmation and does nothing if anything else than a clear yes gets
reported (includes variations of 'No', empty responses and unknown
responses).
This adds folder support as image source, the folder must be specified
in the config file as "Folder" under group "Folder". Parsed images will
be deleted from the folder!
This commit adds a callback which gets called on every
saved Item in the database, which prints JSON of that
Item-object to all connected websocket clients.