Performance tests

[chris-allan]

This PR does a few things:

• Ensures that the performance tests can be run on Windows
• Establishes temporary directory usage, with cleanup, for performance tests
• Expands the performance tests to include read tests
• Enables the performance test as part of the default test suite

If required the performance test can be easily excluded with the surefire plugin:

• mvn test -D'test=!N5BenchmarkTest'

If desired it could also be excluded by default.

While making these changes I noticed that the license on test files is GPLv2. @axtimwalde, was this just an oversight?

[axtimwalde]

Thanks! There are a bunch of changes to the abstract test class in this PR that are unrelated to the performance test and will have downstream effects on other n5 projects (n5-aws-s3, n5-blosc, n5-google-cloud, n5-jpeg, ...?). Should we do this in a separate PR and do in synchrony with the other projects?

[chris-allan]

Absolutely can pull those out when I get a few cycles later tonight/tomorrow.

[chris-allan]

Force pushed away changes to test case base class and opened a new PR #71 for that implementation.