Avoid empty group intro

$group->intro is Null so empty div was displayed.
Handle empty group title to avoid blank tab
Don't show group title if all elements are hidden
Fix bootstrap_tabs template

1. Avoid form.js inserting page divs - not for bootstrap_tabs
2. Put fieldsets into a single tab div per page (form.js no longer
moving these to be together).
Tweak code to make same as bootstrap (no tabs)
Merge pull request #850 from Sophist-UK/fix_form_bootstrap_template_bugs

Fix form bootstrap template bugs