Add @PropertySources and ignoreResourceNotFound

Support repeatable @PropertySource annotations in Java 8 and add
@PropertySources container annotation for Java 6/7. Also add an
ignoreResourceNotFound attribute to @PropertySource allowing missing
property resources to be silently ignored.

This commit also introduces some generally useful methods to
AnnotationUtils for working with @Repeatable annotations.

Issue: SPR-8371
Fix broken test in MvcNamespaceTests

The testDefaultConfig() method in MvcNamespaceTests creates a new Date()
in its test fixture but then performs an assertion against a hard coded
data string of "2013-10-21". This test therefore only passed yesterday,
on October 21, 2013.

This commit addresses this by changing the hard coded date string to one
based on the current date.

Issue: SPR-10665, SPR-8826