Allow leading and trailing newlines in plaintext mail headers and footers

Currently you can't add leading and trailing newlines in mail header and footer templates, which makes is error prone, as users have to remember to add newlines to the beginning or end of the plain-text version of their mail (I'm nu sure this works, as these newlines will probably be removed too).

You can test this by trying to add some leading white space to the default plain-text mail footer (see http://dmaster.demo.civicrm.org/civicrm/admin/component?action=update&id=2 )

The attached patches will fix this (Both CiviCRM and the Quickform package needs fixing).