Add file completion from classpath for @ContextConfiguration

[gayanper]

Expected Behavior
When trying to complete the location on @ContextConfiguration(locations = ".."), provide file completions for xml files from the classpath. Even though most of the configurations are moved to Annotation based configurations, there are some legacy application use xml files to boostrap the application and some tests which use xml files to define the configuration to use for different tests.

[ksankaranara-vmw]

Working on adding this feature

[BoykoAlex]

Merged with 992a7c7