Multiple

Added initial support for multiple choices. …
Still to do:
 - Selectize template
 - Write tests
 - Only tested in Chrome, so other browser tests needs to be done
 - Possibly find a way to remove items from drop down that are currently selected
 - A user provided compare function to determine if an initially selected item matches an item in ctrl.items. Currently uses angular.equals
 - more

Other minor changes
 - Remove Tab key events; they were illogical and prevented ui-select from functioning correctly in a form