Dramatically simplify use of mx_fadable

by applying it to parent elements of things that need to be faded.

src/components/structures/FilePanel.js

@@ -116,7 +116,6 @@ const FilePanel = React.createClass({
                     timelineSet={this.state.timelineSet}
                     showUrlPreview = {false}
                     tileShape="file_grid"
-                    disabled={this.props.disabled}
                     empty={_t('There are no visible files in this room')}
                 />
             );