adds an fallback for APPLICATION_DATA_DIRECTORY

as described in ticket TRUNK-3934: in some deployments using an application server such as Tomcat, we can not write to the current users home dir and instead should use a more generic and/or appropriate path
removed unesseary / from path
Merge pull request #454 from openmrs-codejam-hamburg/TRUNK-3934

TRUNK-3934 - adds an fallback for APPLICATION_DATA_DIRECTORY