Improve application query UI/UX

Summary:
Ref T2625. @chad, you might have some feedback here. The behaviors this implements are:

• When the user selects "Advanced Search", we show the full search UI and no results (for performance and clarity).
• When the user submits a search which is not a named search, we show the full search UI and the "Save Custom Query..." button.
• When the user submits a search which is a named search, we show "Results for search X." with an "Edit Query..." button. The button expands the search form.
• When the user selects a builtin query (like "All Pastes"), we don't show any search UI, but I'm probably going to make this behave more like named searches.

Test Plan:
{F44346}

{F44347}

Reviewers: chad, btrahan, blc

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2625

Differential Revision: https://secure.phabricator.com/D6063