Tagging: use AJAX to populate tags filter widget

This way the list of tags is always kept up to date as tags get added or
removed.
Tagging: fixup table filtering

This is a follow up of ff0127c6292cbe847699c0b9baae30f64444bdab, making
it more robust. Now selecting several tags, then removing them one by
one will re-filter the table each time, previously it was broken.
Tagging: Fix adding/removing tags when filtering is used

The tags would disappear/reappear when resetting the filtering, because
we were not updating the master table.