loading indicator for support webpages

[jenn-chaulk]

From jchaulk created by jenn-chaulk : #1

From focus-ios created by lime124 : mozilla-mobile/focus-ios#575

When our UI loads a webpage, as in the case of What's New or Help, there is not a loading indicator shown so you are looking at a blank, black page wondering what's going on.

This issue is to address showing a loading indicator for any support type webpage we point to in our app. (accessed via settings, not the general browsing UI).