Fix scrolling of query items and JSON details view

Summary: This diff fixes the tripple scrollbars in the graphQL plugin, and makes sure scrollbars for the detail panel are properly shown

Reviewed By: jonathoma

Differential Revision: D21177849

fbshipit-source-id: d40173d7e9a45064b608c8d953c7aea47a4acd0f

desktop/app/src/PluginContainer.tsx

@@ -55,7 +55,7 @@ const Container = styled(FlexColumn)({
 export const SidebarContainer = styled(FlexRow)({
   backgroundColor: colors.light02,
   height: '100%',
-  overflow: 'scroll',
+  overflow: 'auto',
 });
 
 const Waiting = styled(FlexColumn)({