Be careful syncing $location.search and queries

We shouldn't sync the URL bar with the search query on every route
update because some routes may have query parameters that are
irrelevant for search, such as the editor.

Instead, sync them whenever the StreamSearch or (Page)Search route
controllers initialize.

Fix #1339
Merge pull request #1340 from hypothesis/1339-careful-location-search-sync

Be careful syncing $location.search and queries