Multiple tags support

[monadli]

It seems BT only allow one tag for each resource. It may be easy to support multiple tags in the existing tagging popup.

If we use comma as tag separator, then "photo, New York" for a picture has two tags "photo" and "New York".

Saving does not need to change at all.

On side panel display though, besides existing display as "photo New York" as a tag by removing comma, two separate tags "photo" and "New York" can be displayed as well, and since there are resources with "photo, New York", so under "photo", show another tree node for "New York". Same for "New York", show a subtree for "photo".

By doing this, this tool will be way easier to use and organize resources. People just tag as "photo, Washington D. C.", then dynamically under "photo" there will be both "New York" and "Washington D. C.", etc.

By doing this, without any file save change at all, just change UI to display more dynamic display of tags, it will be easier to navigate following tags.