Relaxing the requirement that users specify a loading indicator image resource.  If the image resource is null, the table will not create a default loading indicator.

Review at http://gwt-code-reviews.appspot.com/1349801

Review by: jasonmheim@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9692 8db76d5a-ed1c-0410-87a9-c151d255dfc7