More image formats, filtering, sorting, and updating

This MR affects quite a bit of the functionality of the loading of images, the structure of the database, and how the application function.

• Update to database structure. The new structure is incompatible with the old, but IMHO the structure is more consistent.
• Added possibility to filter and sort the ImageList.
• Added possibility to tag images.
• The list of images automatically reloads on database changes and the separate images update on local database changes.
• Added possibility to hide images.
• Loads all known hashes on loading of UploadImage.html. The effect of this is that when you update a pdf for the second time, it will only take the images that are not already in the database.
• Added support for extracting JPEG images from pdfs. A bit hacky at the moment, and creates two canvases, potentially reducing speed significantly.
• Apply operations (Hide/Unhide, Add/Remove tags, Delete) to all shown photos

Potential improvements:

* [-] Add filter to db.changes call in ImageList.html to only react to: removals and insertions of images, and change in hidden status. Currently the full list is reloaded on any database change.