Address API Review for SettingInjectorService

- Escape < and > in javadoc

- Constructor does not take log tag

- Start intent rename

- Comments for Status.summary and enabled

- Bonus fixes:

  - Start renaming STATUS_KEY to SUMMARY_KEY

  - Send message back even if getting the status fails so we don't have
  to wait for the fetch to time out

  - Add comment about setting activity being invoked when disabled

- Partial fix for b/10461474

Change-Id: I025e7e0782c2873a4eda20ab4793bc6145daf8db