Use pytest to bring OmeroWeb unit tests in line with OmeroPy

Unit tests for OmeroWeb can now be run with:

    ./build.py -f components/tools/OmeroWeb/build.xml test
Allow instantiation when config.xml is missing

If config.xml is missing it should still be possible to run through our
Django settings configuration.  An empty dictionary of settings
should suffice.
Fix flake8 errors in setup.py
Add tools/target/lib/python to setup.py
Added test_simple as a smoke test from OmeroPy/test/integration/
Add OmeroPy to the PYTHONPATH in setup.py

This allows us to use the OmeroPy integration test libraries, fixtures
and infrastructure in the OmeroWeb tests.
More robust searching for the OmeroPy directory
Add a README to mainly document test running
Update integration test target
Fix flake8 errors
Ensure components/tools/OmeroWeb/test/unit is hitting flake8
Also run OMERO.web unit tests
Merge remote-tracking branch 'origin/dev_5_0' into omeroweb-test-fixes

Conflicts:
	components/tools/travis-build
Fix flake8 errors
Use flake8 on all of components/tools/OmeroWeb/test
Ensure basic OMERO.web environment is completely set up
Switch from DOS to UNIX line endings
Make "integration" target only run integration (not unit) tests

With this commit OmeroPy and OmeroWeb "integration" targets from
`build.py` or Ant will only run integration tests.  This mirrors the
documented behaviour of using `setup.py` directly for either tools
component.  Collisions, where both a unit and integration test package
have the same name, are possible in the global build without this
change.
Switch marshaling tests over to pytest
Merge pull request #2319 from chris-allan/omeroweb-test-fixes

OMERO.web unit and integration test fixes