Move common scss mixins to common/static/sass, and tweak the video player to…

Move common scss mixins to common/static/sass, and tweak the video player to have more in common between the cms and the lms

cms/static/sass/_mixins.scss

+../../../common/static/sass/_mixins.scss
\ No newline at end of file

cms/static/sass/base-style.scss

@@ -3,6 +3,7 @@
 @import 'keyframes';
 
 @import 'reset';
+@import 'mixins';
 @import 'base', 'layout', 'content-types';
 @import 'calendar';
 @import 'section', 'unit', 'index';

common/lib/xmodule/xmodule/css/video/display.scss

@@ -5,6 +5,7 @@ div.video {
   margin: 0 -12px;
   padding: 12px;
   border-radius: 5px;
+  font-size: 16px;
 
   article.video-wrapper {
     float: left;

lms/static/sass/base/_mixins.scss

+../../../../common/static/sass/_mixins.scss
\ No newline at end of file