angular-slider unbinds all event listeners from document

[viktor-shepel]

angular-slider directive unbinds all mousemove and mouseup event
listeners from the document when user finish sliding, thus effectively
unsubscribe rest of the code from aforementioned events. In order to
preserve external listeners only own event handlers are unbinded.

bug can be reproduced here - https://jsfiddle.net/8c31mpyd/
pull request - #32