better handles cells for Helpshift enabled status

@sendhil - reissuing pull for 4.2.  replaces #2033 

This should fix the case where Helpshift was always loaded. On the baseline, SupportViewController was displaying the FAQ from Helpshift (which also includes a button for Contact Us). On the experiment, it was showing only the Contact Us cell.

This PR brings back the FAQ and Help Center pages if on the baseline and adds a FAQ cell on the Helpshift experiment.

closes #1866