Add five seconds step to video slider

Currently, video is moving one second ahead or behind on each right
and left arrow key respectively.In order to make it compliant with
the industry standards like Youtube,its step is adjusted to five
seconds.

PROD-159

common/lib/xmodule/xmodule/js/spec/video/video_progress_slider_spec.js

@@ -30,7 +30,8 @@
                         min: 0,
                         max: null,
                         slide: state.videoProgressSlider.onSlide,
-                        stop: state.videoProgressSlider.onStop
+                        stop: state.videoProgressSlider.onStop,
+                        step: 5
                     });
                 });
 

common/lib/xmodule/xmodule/js/src/video/06_video_progress_slider.js

@@ -120,6 +120,7 @@ function() {
             edx.HtmlUtils.HTML('<div class="ui-slider-handle progress-handle"></div>')
         );
 
+        // xss-lint: disable=javascript-jquery-append
         this.videoProgressSlider.el.append(sliderContents.text);
 
         this.videoProgressSlider.slider = this.videoProgressSlider.el
@@ -128,7 +129,8 @@ function() {
                 min: this.config.startTime,
                 max: this.config.endTime,
                 slide: this.videoProgressSlider.onSlide,
-                stop: this.videoProgressSlider.onStop
+                stop: this.videoProgressSlider.onStop,
+                step: 5
             });
 
         this.videoProgressSlider.sliderProgress = this.videoProgressSlider
@@ -327,6 +329,7 @@ function() {
                     msg = ngettext('%(value)s second', '%(value)s seconds', value);
                     break;
                 }
+                // xss-lint: disable=javascript-interpolate
                 return interpolate(msg, {value: value}, true);
             };