added title tooltip to CollapsableControls

src/mol-plugin-ui/base.tsx

@@ -96,7 +96,7 @@ export abstract class CollapsableControls<P = {}, S = {}, SS = {}> extends Plugi
         return <div className={wrapClass}>
             <div className='msp-transform-header'>
                 <Button icon={this.state.brand ? void 0 : this.state.isCollapsed ? 'expand' : 'collapse'} noOverflow onClick={this.toggleCollapsed}
-                    className={this.state.brand ? `msp-transform-header-brand msp-transform-header-brand-${this.state.brand.accent}` : void 0}>
+                    className={this.state.brand ? `msp-transform-header-brand msp-transform-header-brand-${this.state.brand.accent}` : void 0} title={`Click to ${this.state.isCollapsed ? 'expand' : 'collapse'}`}>
                     {this.state.brand && <div className={`msp-accent-bg-${this.state.brand.accent}`}>{this.state.brand.name}</div>}
                     {this.state.header}
                     <small style={{ margin: '0 6px' }}>{this.state.isCollapsed ? '' : this.state.description}</small>