Summary:
Mock routes may contain quite a bit of data for header values and response bodies. Currently, to turn off a mock a user must delete the mock and then go through the process of creating it when needed again. This change will allow a user to temporarily disable a mock without deleting it.
A checkbox on the Routes list is used to enable/disable mocks. As shown in this screenshot:

## Changelog
Network Plugin - disable/enable mock routes
Pull Request resolved: https://github.com/facebook/flipper/pull/1969
Test Plan:
Create mocks using sample app
Verify that mocks are working as expected
Disable the mocks
Verify that the client has been updated with mocks (minus the disabled ones) user Flipper Messages plugin
Use the sample app to send the disabled requests again and verify that they are not mocked
Reviewed By: mweststrate
Differential Revision: D26888815
Pulled By: passy
fbshipit-source-id: cb8a05a27dd69ba4d2b60085a077efe795a99a7c