Search box: search icon, and other improvements

This incorporates a number of changes to the search box, as suggested by
Jennifer:

* Add a search icon to allow click-to-search.
* Slightly shrink the search text.
* Change the search text from "search reddit" to just "search".
* Add more padding.
* Remove the now-redundant search button on the search results page.

It also adjusts the login box style to match.
static build: Put nymph output in css/ subdirectory.

This keeps nymphified and unnymphified LESS inputs in the same location
so that "../whatever.png" references work with uncompressedJS true or
false and we can use the LESS `data-uri` function.