Summary:
Fix selection problem on ManageMockResponsePanel. Currently, when the user adds new routes, the detail section continues to show the detail for the first route. Select different routes in the list does not change the detail panel. The screen is currently not doing anything on selection.
Also fixed a problem with updating on mock header names and values. Updates were not persisting if user did not exist input fields before leaving header input panel.
## Changelog
Network Plugin - Fix selection problem on ManageMockResponsePanel
Pull Request resolved: https://github.com/facebook/flipper/pull/2574
Test Plan:
Add multiple mock routes
Select various routes
Verify that detail panel shows the selected route

Reviewed By: passy
Differential Revision: D29582286
Pulled By: mweststrate
fbshipit-source-id: 6690e2262a033cdfa5afa6e6fdfacc9694244590
Summary:
Changelog: Updated Network plugin to Sandy UI, including several UI improvements
Converted UI to Sandy, and some minor code cleanups
Moved all mock related logic to its own dir
Fixes https://github.com/facebook/flipper/issues/2267
Reviewed By: passy
Differential Revision: D27966606
fbshipit-source-id: a64e20276d7f0966ce7a95b22557762a32c184cd