Make the TableSelector header match the mockup.

Make the TableSelector header match the mockup.

* src/main/java/org/glom/web/client/OnlineGlom.java: Add a margin to
the layout panel. Properly lineup the table selection header with
the list and details view.
* src/main/java/org/glom/web/client/ui/DetailsViewImpl.java: Remove the
margin around the details view.
* src/main/java/org/glom/web/client/ui/TableSelectionViewImpl.java:
Rename listBox variable to tableSelector. Set id for the style sheet.
Use a FlowPanel instead of a HorizontalPanel.
* src/main/webapp/style.css: Add properties to make the TableSelector
box match the mockups.