added unit testing framework googletest 1.7.0 and a first example test

Hello,

I'd like to add some unit tests to e.g. the meterD0 code. 
I added googletest 1.7.0 framework and one example test including travis-ci execution. Let me know what you think about it or whether you have any better idea to integrate a test framework without putting it into the source tree.

Matthias