DAR-2618 removed unnecessary file extensions
added .inactive class in modal_default.scss
added activate() and deactivate() methods to modals' API
small refactoring, added disabling modal buttons
small refactoring and added isActive() method to modal API
added jQuerySelector var to fix JSHint issue; fixed a bug in activate() method
DAR-2618 added different opacity for deactivated modal
DAR-2618 used new modal API methods