Show the search navbar when searching for `pool:1234 tag`. Before the
search navbar would always be hidden if the search contained a pool:
metatag, even if it was a multi-tag search.
Fix the pool name not being bolded in the pool navbar when doing a
pool:<name> search. Previously the selected pool was only bolded when
doing a pool:<id> search.
* Factor out the post navbar into a component. The post navbar is the
part of the post containing the current search, the list of pools, and
the list of favgroups, along with next/prev navigation links.
* Change navbar markup: remove various unused CSS classes/IDs, change
pools to use same markup as favgroups, replace nested <div>'s with
flat <ul>/<li> list.
* Use CSS to truncate long searches/pool names/favgroup names if they're
too wide for the screen (especially on mobile).
