Omero-metadata

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* Update the source code to be flake8 compliant
* Activate the metadata and table integration tests in Travis

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This is the first release deployed to PyPI

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This release contains the metadata code matching the state of OMERO 5.4.7.

* Add metadata code filtered from the develop branch of
openmicroscopy/openmicroscopy
* Remove OMERO_DEV_PLUGINS variable
* Add infrastructure for releasing the module to PyPI
* Activate Travis CI for running the integration tests using omero-test-infra

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* Filter metadata code from the metadata53 branch of
openmicroscopy/openmicroscopy