Refresh the emoji library (#7001)

* refresh the emoji library

* fix img_trans.gif

* compress sprite sheet

* remove note on compression - webpack seems to handle compression decently

* better emoji sheet preloading

* requested changes

webapp/components/create_comment.jsx

@@ -17,6 +17,7 @@ import MsgTyping from './msg_typing.jsx';
 import FileUpload from './file_upload.jsx';
 import FilePreview from './file_preview.jsx';
 import EmojiPickerOverlay from 'components/emoji_picker/emoji_picker_overlay.jsx';
+import * as EmojiPicker from 'components/emoji_picker/emoji_picker.jsx';
 import * as Utils from 'utils/utils.jsx';
 import * as UserAgent from 'utils/user_agent.jsx';
 import * as GlobalActions from 'actions/global_actions.jsx';
@@ -588,6 +589,7 @@ export default class CreateComment extends React.Component {
                     <span
                         className={'fa fa-smile-o icon--emoji-picker emoji-rhs'}
                         onClick={this.toggleEmojiPicker}
+                        onMouseOver={EmojiPicker.beginPreloading}
                     />
                 </span>
             );