Add manual state for popover

The manual state is used in the docs, but is not implemented. Using this popover will properly listen to setting the visiblity state on mount

Author: Adnan Oner

src/popover/Popover.jsx

@@ -58,6 +58,8 @@ export default class Popover extends Component {
 
       popper.addEventListener('mouseenter', this.handleMouseEnter.bind(this));
       popper.addEventListener('mouseleave', this.handleMouseLeave.bind(this));
+    } else if (trigger === 'manual') {
+        this.setState({ showPopper: this.props.visible });
     } else {
       if (this.reference.nodeName === 'INPUT' || this.reference.nodeName === 'TEXTAREA') {
         this.reference.addEventListener('focus', () => { this.setState({ showPopper: true })});
@@ -139,7 +141,7 @@ export default class Popover extends Component {
 Popover.propTypes = {
   width: PropTypes.oneOfType([PropTypes.number, PropTypes.string]),
   placement: PropTypes.oneOf(['top', 'top-start', 'top-end', 'bottom', 'bottom-start', 'bottom-end', 'left', 'left-start', 'left-end', 'right', 'right-start', 'right-end']),
-  trigger: PropTypes.oneOf(['click', 'focus', 'hover']),
+  trigger: PropTypes.oneOf(['click', 'focus', 'hover', 'manual']),
   title: PropTypes.string,
   content: PropTypes.oneOfType([PropTypes.node, PropTypes.string]),
   popperClass: PropTypes.string,