Add additional predefined Date/Time formats and the ability to generate custom localized formats.

Public review at: http://gwt-code-reviews.appspot.com/578801

Patch by: jat
Review by: jlabanca


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8252 8db76d5a-ed1c-0410-87a9-c151d255dfc7