[toolchain] enable history across saves, closes #106

conda/js/src/components/toolchain/ToolchainEditor.jsx

@@ -139,10 +139,7 @@ export class ToolchainEditor extends React.PureComponent<Props, State> {
 	componentWillReceiveProps = (nextProps: Props) => {
 		this.setState({
 			cache: getValidObj(nextProps.data),
-			history: {
-				past: [],
-				future: [],
-			},
+			history: generateNewHistory(this.state),
 		});
 	}