Adjust oauth cordova warning.

* Show only for oauth2, since oauth1 (twitter) works everywhere now.
* Show on all platforms except ios simulator, since oauth2 is somewhat
  broken everywhere except ios simulator.
* Reformat to match the local-network warning.
Tweak cordova oauth warning wording
Link to mobile oauth wiki instead of saying UIWebView
Update Facebook oauth instructions
Don't show login configuration dialog on cordova