java: Add nucleotide-count exercise

Use fest-asserts in the test which offers additional clarity in the
expectations.

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Merry Christmas :-)

I'm not a biologist but I found myself confused about nucleotides vs nucleosides (e.g., cytidine vs cytosine). I kept the names as is but I always thought that 'C' should be [cytosine](http://en.wikipedia.org/wiki/Cytosine) and 'T' should be [thymine](http://en.wikipedia.org/wiki/Thymine).

Also, the tests don't preclude the idea that counting a DNA string like "hello world" will do something odd but that seems to be the case in other implementations as well.

For the Java folk, I would be curious about porting the other exercises to fest-asserts as well. I like them better than the JUnit native hamcrest matchers, even though they are an additional dependency. (Compare this to the robot-names tests.) Thoughts?