feat(jqm-class): add jqm-*-class directives,refactor theme handling

    * jqm-position-class directive - adds class based on position
    * ng-click decorator - adds ui-btn-up-<theme> and ui-btn-down-<theme> classes
    * jqm-once-class directive - adds a class once after interpreting (no
     watch)
    * adds scope.$theme property and jqmConfig service for default theme.
    * removes jqm-theme-class directive and serivce - use scope.$theme