* new diffexp REST API spec
* new diffexp REST API; faster diffexp and dataframe slicing
* first draft of fast diffexp
* convert variance calculation to two-pass method
* lint
* update front-end use of API
* fix typo in spec
* disable content compression
* catch index filter format errors
* clean up of dead code
* resolve PR review comments
* Create Release_Validation_Recipe.md
* compose middle ware for redux devtools
* update package.json and lock
* remove heatmap, add to left side bar
* redux devtools extension
* Use HTTPStatus for all responses
More informative than just the code as an int
* Fill out REST error handling
* Test error routes
* Use HTTP Status for tests too
* factor mime type request into function
* Better mimetype errors
* 404 -> 400 error for bad key
REST API now requires that the server sort all dataframe responses by dimension index (var or obs index), allowing the client (front-end) to assume responses will be sorted. Given that the dataframe usually has a natural ordering, and the server gets to arbitrarily assign indices, this is the most computationally efficient design.
This PR includes changes to the REST API spec, and removing the explicit sort in the front-end code.
