Make cctray_xml_feed_mock able to accommodate custom scenarios

[GentlemanHal]

Allow programmatic setting of CCTray XML data

This would allow tests to explicitly set the data they wished to be returned which would make them easier to read and update.

Extract into its own package

This would make it easier for any one to use who wants to test CCTray XML feeds. For example we could use it test clj-cctray directly.