Edit Dashboard title and Slice title in place (#2940)

* Edit Dashboard title and Slice title in place

Add EditableTitle component into Dashboard and Explore view to support edit title inline.

superset/assets/javascripts/dashboard/components/SaveModal.jsx

@@ -79,6 +79,7 @@ class SaveModal extends React.PureComponent {
       positions,
       css: this.state.css,
       expanded_slices: expandedSlices,
+      dashboard_title: dashboard.dashboard_title,
     };
     let url = null;
     if (saveType === 'overwrite') {