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
Updating docs links on Javadoc front page
"Show file paths" now shows the targets of the (sym)links in case of inplace imports
Externalized the FilePath dialog into a separate class
Implemented a clickable tooltip
Improved/Fixed inplace import icon tooltip/paths

Swing tooltip replaced by ClickableTooltip
'Show file paths' now shows the link target in case of inplace imports