Merge Histogram ROI to microns

[alexbaden]

Adds histogram ROI service, fully documented + tested.

Note that this also moves the histogram data out of the nduser django app and into the stats django app. You will need to run python manage.py migrate after pulling these code changes on all ndstore installations.

[kunallillaney]

@alexbaden this looks great. I do need three things before we can merge this into microns.

• [x] Fix the urls.py for django1.8/django1.10 update. You can look at the spdb/urls or catmaid/urls in microns branch for reference
• [x] Update the README.md in the tests folder with any new tests you have added. This is a good reference document to keep tabs on which tests exist. I think there should be no action needed here but just recheck.
• [x] The merge the latest version of microns with ab-histogram to resolve any conflicts.(My guess is that is not necessary since there should be no merge conflicts but just in cas)

Thanks.

[alexbaden]

All done and pushed. I am running tests on brainviz now, where this branch is deployed. I'll let you know once I have a result there.

[kunallillaney]

@alexbaden I will merge this in. I don't think all the tests will pass since @randalburns catmaid push. Some of the tile_api functions have changed and the tests will have to be updated for that. Thanks.