R1:19db3fbb605c

Allow merchants to disable payment providers and show more UI info

Summary:
Ref T2787.

- Allow merchants to disable payment providers.
- Show more useful information about providers on the payments page.
- Make test vs live more clear.
- Show merchant status.
- Add a description to merchants to flesh them out a bit -- the merchant areas of responsibilities seem to be fitting well with accounts, etc.

Test Plan: {F215109}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley…