Unify versions in POMs started by the invoker

Unify the versions used in integration tests launched by the
maven-invoker-plugin. Allows for already cached local copies to be
used, hopefully speeding up the build.
Fix URL methods in JarURLConnection

Update JarURLConnection to return correct values from `getURL()`,
`getJarFileURL()` and `getEntryName()`.

Fixes gh-973
Fix Jasper on Tomcat 8

Refactor Jasper initialization code to call JasperInitializer during
server start.

Fixes gh-962
See gh-919