[tag tool] Large feature to support applying a new tag to the whole library

ATM the tag tool is best for editing existing tags. Recently @m4rc1e added a simple form input to add a new tag string, which results in an empty tag set list.

But what we need as a workflow, is a (large) feature in the tool to show all 1,700+ families and allow rapid-fire tag data creation at that scale.

For some tags, we need to be library-complete, and so need a workflow for going over all 1,700+ families. My guess is that we could use hotkeys so that eg pressing `tab` (using HTML tabindex properties) moves us directly to the next row's input box, `backspace` or `space` makes that family have a zero value (and thus disappears and doesn't appear in the CSV output), and with a desktop keyboard number pad for a right handed person, the workflow can be super fast where they tap `tab` with a left hand finger, `space` with a left hand thumb, and numbers on the numberpad with the right hand.

But for other tags, we can use existing tags to exclude some existing tags - we can say confidently that "anything with previously existing tag X will have a new tag Y value of 0 and therefore can be excluded from this workflow".

Likewise we might want to say "anything with previously existing tag X will have a new tag Y value of X and therefore can be included for this workflow starting with that value and then I'll edit it from there".