Fixes search weirdness (take 2).

* Updates search results when performing a second search while first is still showing on the screen.
* Uses .replace() to ensure new results fragment is shown each time and does not add transaction to back stack.
* Explicitly removes pager results fragment when search is collapsed rather than relying onBackPressed().
Merge pull request #31 from mapzen/fix-search-weirdness-take-2

Fixes search weirdness (take 2).