Add option to keep casing of report testname

[karlveezoo]

Currently the testname is put to lower case here:

scalac-scoverage-plugin/runtime/shared/src/main/scala/scoverage/Invoker.scala

Line 82 in 15b5604

.map(_.getClassName.toLowerCase)

I have a use case where I would like to keep the proper casing of the test. Would be great for an option to switch this functionality