Rewrite the tag counter widget (the one above the tag edit box) to use
React. This is a trial run for using React elsewhere.
We actually use Preact instead of React because it's lighter weight.
We use Mobx for state management because it's cleaner than React's
setState or useState.
This incidentally fixes a couple bugs:
* The tag counter wasn't updated when deleting tags with backspace
* The tag counter wasn't updated when pasting in new tags.
This was only used on the saved search index. It let you click on column
headers to sort the table by that column. This doesn't make sense now
that saved searches are paginated.
Add the following fonts:
* Comic (Comic Relief)
* Slab Sans (Anton)
* Slab Serif (Rokkitt)
* Formal Serif (Lora)
* Formal Cursive (Petit Formal Script)
* Print (Kalam)
* Hand (Indie Flower)
* Narrow (Archivo Narrow)
* Blackletter (Unifraktur Maguntia)
Add the following font aliases:
* Comic Sans MS is aliased to Comic Relief.
* Arial Narrow is aliased to Archivo Narrow.
* Rockwell is aliased to Rokkitt.
* Impact is aliased to Anton.
Very old browsers (in particular, Firefox 16 and iOS 8.4 Safari) don't
support flexbox without prefixes, which breaks sidebar and comment
layouts. Extend the browserlist config so that autoprefixer generates
flexbox prefixes for these browsers.
