Allow searching in a thirdparty folder for vendor jar files

This means that the maven copy-dependencies jar-with-dependencies goal can have
its output entirely placed into the `thirdparty` folder, making deployment easier.
This stops conflicts with the existing oncue-agent dependencies in the `lib`
folder of the microkernel that I was finding when trying to deploy a deb package
containing jars directly into the `lib` folder of an oncue-agent deployment that itself
was packaged as a deb.

Note: This may cause issues if the thirdparty libraries depend on a different
version of the oncue-agent core libraries (e.g. logback), as there will be
multiple versions of some classes on the classpath. The wildcard jar inclusion
will mean the classloader loads the class from the first jar defining it that is 
included on the classpath. This issue also exists in the current version when
placing your dependencies in the `lib` folder.