Update the search scope selector after Quicksand navigation

Summary:
Fixes T7900.

• Update the hidden form input so the current application is searched.
• Update the menu icon.
• Update the button icon, if "Search Current Application" is selected.

Test Plan:

• Navigated between applications with Quicksand.
  • Observed button icon update.
  • Observed menu icon update.
  • Observed results being scoped to the correct application.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7900

Differential Revision: https://secure.phabricator.com/D12540