Implement improved multiple-select widget for Groups and Tags selection

Example of the new widget:
http://www.ryancramer.com/projects/asmselect/examples/example1.html

If time allows, scope may expand to include:

• Add to Group interface (contact Groups tab and batch Add to Group action)
• CivMail Select Recipients form (Include / Exclude Groups, and Include / Exclude Prior Mailings fields)
• Enable Components form (Admin >> Global Settings)
• Case Type and Activity Type multi-selects in Advanced Search and corresponding component searches (NOTE: multiple select for activity types is being implemented in trunk for 3.2)