[tests] basic pytest setup
[tests] fix grid tests
[tests] comment out non-functional test
[tests] update dependencies
[tests] only consider src/pymortests for test discovery
[tests] single module testing uses pytest too now

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[tests] more py.test plugins

running a single test by calling its test file does not yet work
[travis] only notify on changing build status
[setup] beat setuptools into including pyx sources in sdist
[tests] tox works (at least the py27 env)

simply call 'tox -e py27' in pyMor's root dir
[tests] add coverage output