Add new field "description" to civicrm_relationship

Add a new field "description" to civicrm_relationship and add view/edit/create operations to all places where relationships are edited/viewed etc (I suspect in all the places as start date/end date).

We will need to backport this to v1.4 for a couple of users, so can we please do this as a clean one shot commit (i.e. all the needed changes only are present in this commit, no more/no less). If not possible, please make sure you tag all your commit with the issue number so we know what files have changed