Add Clover check to maven build

[Ali Kord]

Make maven verify run Clover checks by default, however, according to the Clover2 plugin docs:

As Clover integration produces instrumented classes, we recommend to ensure 
that you do not install them to production (for instance: 'mvn deploy' to public 
repository, 'scp' to an application server running on production, etc). Having 
instrumented code in such location(s) is usually not desired.

Common practices to ensure proper separation of instrumented and 
non-instrumented classes and JARs are:

1. configure Clover in a profile in your pom.xml
...

So, we add clover checks to a profile (e.g. "clover.all") and run the test using mvn verify -Pclover.all which is still easier to remember than the full clover plugin command.

[Ali Kord]

Open source Clover license obtained and added to the project.

[Anund McKague]

Clover can now be run from any module.