Allow uberjar to place the project jar at the beginning of the classworlds conf file

Due to how resource resolution occurs within the classloader, sometimes it is advantageous to have the project jar placed earlier in the classworlds configuration for uberjars.

I.e. If I want my project resources to override another projects (eg META-INF/service, or log4j or any other of a myriad) then I need my project jar occurring at the start of the classworlds conf.

To this end,

Add a property (this name is only an example - it should be shortened)
maven.uberjar.project.jar.position=first

(domain = first | last) default should be last to remain consistent with existing configuration.