Set default values for allowed html and iframesi #1056

This avoids errors if upgraders don't update config.php

Conflicts:

	application/hooks/2_settings.php
Merge branch '2.7b' into develop
Merge branch '2.7b' of https://github.com/ushahidi/Ushahidi_Web into develop
Merge branch 'master' into develop
Merge branch 'master' into develop
Merge remote branch 'upstream/master' into develop