added linkify filter and linkify tests

Hi just thought of adding linkify filter for string. Angular has built in linky filter but not playing well with combination of using ng-bind-html in which data to be binded is an html format. Angular linky only takes plain text input and converts to links, but when input is HTML, the linky filter works well but the ng-bind-html stops working. ref#: http://stackoverflow.com/questions/17541305/angularjs-possible-to-sanitize-and-linky-in-same-directive

In addtion, this linkify filter supports domain links, ftps and emails.