support the creation of a CMS user from a contact record

the attached patches add an option to create a CMS user account from within a civicrm contact record.
the link is found in the actions dropdown, where the user record link would be (if an existing linked user exists).

most of my testing was in joomla, so during QA, we should be sure to test drupal. it makes use of the existing BAO functions to create users, so it should work seamlessly with both.

the only thing not really addressed is permissioning. since the relevant perms are outside of civi, i'm not sure the best way to build the menu access params such that it accounts for both joomla and drupal