Drupal views: Set preferred_communications_method to use pseudoconstant handler

The preferred_communications_method field currently displays as an integer. The attached patch sets this field to use the pseudo_constant handler.

This patch also amends the pseudo_constant handler to handle the case where multiple values are separated by 0x01 values (as far as I know, preferred_communications_method is the only case where this is currently used). My testing shows this works fine in the case where fields hold a single (non 0x01-separated) value.

This patch also disables the ability to sort, filter and use arguments on the preferred_communications_method, as there is currently no code (that I'm aware of) the modifies to the views query to cater for multiple value fields. Sort, filter and arguments previously existed, but I think they must have been failing to work correctly for this reason.