Switch from romanesco to girder_worker

[cdeepakroy]

@brianhelba .travis.yml needs to be updated to switch from romanesco to girder_worker

[brianhelba]

@manthey Can you convert all of this plugin to use girder-worker instead of romanesco?

You can do this here in HistomicsTK after you finish the same task in large_image.

[manthey]

It looks like this needs to install some dependencies: openslide-python, scikit-learn, and nimfa from pip, and python-skimage from apt-get. Versions appear important -- when I've installed all of these and try to process an image, I get an exception fromstring() has been removed. Please call frombytes() instead. I think this means that some module wants an earlier version PILLOW.

[cdeepakroy]

@manthey All dependencies based on c libraries are in the requirements_c.txt which is where nimfa should go i think. All dependencies that are not based on c libraries go in requirements.txt.

I had to do this separation because ReadTheDocs (that we use to auto-generate documentation) doesn't work if install_requires in setup.py has c-dependent libraries. So, I add the dependencies within requirements_c.txt into install_requires in setup.py only if python setup.py install is not run on ReadTheDocs. Also for ReadTheDocs to work i have to add mocks for all imports of all modules from c-dependent python packages. This is very convoluted and annoying. I wish there was a better way to do this.

Also, .travis.yml should pip install requirements_c.txt as i have pointed out in this issue.

For openslide i guess we also have to do apt-get install openslide-tools as mentioned in this webpage. Dont know if we can apt-get install python-openslide instead of pip installing it. I guess if .travis.yml creates a virtual environment with access to system site-packages then we can apt-get install it instead of pip install.