UI for controls.

- Make backend address configurable via env variable
- `BACKEND_HOST=1.2.3.4:4040 npm start` points the frontend to the app on that server. Just for development
- Render control icons
  - removed close x for details panel
  - added control icons in its space
  - closing of panel still works by clicking on same node, or background
- Dont allow control while pending
- Render and auto-dismiss control error
- Make tests pass

client/app/scripts/components/node-control-button.js

@@ -0,0 +1,23 @@
+const React = require('react');
+const AppActions = require('../actions/app-actions');
+
+const NodeControlButton = React.createClass({
+
+  render: function() {
+    let className = `node-control-button fa ${this.props.control.icon}`;
+    if (this.props.pending) {
+      className += ' node-control-button-pending';
+    }
+    return (
+      <span className={className} title={this.props.control.human} onClick={this.handleClick} />
+    );
+  },
+
+  handleClick: function(ev) {
+    ev.preventDefault();
+    AppActions.doControl(this.props.control.probeId, this.props.control.nodeId, this.props.control.id);
+  }
+
+});
+
+module.exports = NodeControlButton;