Revert "Improve backward compatibility of the template"

This reverts commit 7fbacf4d4e543bbdf9d989dac43faeb5cea75255.
The template is question still hangs on SilverStripe 3.0.5.
Require silverstripe 3.1

There is a bug in SilverStripe 3.0.5: comments (<%-- --%>) cannot be
multiline. I use multiline comments everywhere, so I prefer to just drop
backward compatibility on the 3.0 branch.
Update bootstrap to 3.3.1