Debian packaging improvements

Some small changes to make the Riemann deb nicer to work with.
Could you clarify why we should move from /usr/lib to /usr/share? The jar is the Riemann library, and the [FHS](www.pathname.com/fhs/pub/fhs-2.3.html#USRLIBLIBRARIESFORPROGRAMMINGANDPA) says "/usr/lib includes object files, libraries, and internal binaries that are not intended to be executed directly by users or shell scripts.", whereas [/usr/share](www.pathname.com/fhs/pub/fhs-2.3.html#USRSHAREARCHITECTUREINDEPENDENTDATA) is for "architecture-independent data files".