Set table headers when table dropBox changes.

 Set table headers when table dropBox changes.

 * src/org/glom/web/client/GlomDocument.java: Correct some method
 names.
 * src/org/glom/web/client/LibGlomService.java: Add method
 to get list layout field names.
 * src/org/glom/web/client/LibGlomServiceAsync.java: Add method
 to get list layout field names.
 * src/org/glom/web/client/ListLayoutTable.java: New file - composite
 widget for list layout table.
 * src/org/glom/web/client/OnlineGlom.java: Add a change handler for
 the table drop box and add new updateTable() method to asynchronously
 get the layout list field names for the currently selected table.
 * src/org/glom/web/server/LibGlomServiceImpl.java: Add server side
 implementation of getLayoutListHeaders() method.
 * war/OnlineGlom.html: Remove GlomWebApp div tag as it is not required.