static/frontend/search: fix search bugs
static/frontend/search: fix search bugs

- Fixes the more results link by passing in search mode
instead of an empty string. When the pagination.URL
function is called without the m param set, it uses
the value from the previous call.

- Uses plural tab names.

Change-Id: Ic5596d0bc80c06daebba75fa5638f34bb75c5545
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/347405
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite