added 20x20 images so images in the users window don't shift

bigbluebutton-client/src/org/bigbluebutton/common/Images.as

...ient/src/org/bigbluebutton/common/assets/images/audio.png

...t/src/org/bigbluebutton/common/assets/images/audio_20.png

...org/bigbluebutton/common/assets/images/audio_muted_20.png

...lient/src/org/bigbluebutton/common/assets/images/lock.png

...nt/src/org/bigbluebutton/common/assets/images/lock_20.png

...ent/src/org/bigbluebutton/common/assets/images/unlock.png

.../src/org/bigbluebutton/common/assets/images/unlock_20.png

.../bigbluebutton/modules/users/views/MediaItemRenderer.mxml