Tox regression testing (simplified implementation)

[markrtuttle]

This adds tox regression testing to viewer. Tox is the standard python tool for testing packaging, testing installation, and running regression tests, potentially with many different versions of python, etc.

This adds regression tests that clone the coreHTTP repository, breaks the proofs, runs all the proofs, and compares the html and json output against expected output.

This pull request should be reviewed by commits:

• First commit modifies viewer to produce sorted json output to make it easier to compare output of different runs.
• Second commit adds about 1700 files that are the expected output for the coreHTTP proofs (no need to review this data)
• Third commit add the coreHTTP regression tests
• Fourth commit adds the tox.ini file that drives the tox regression testing

Note that this is a lot of data in the second commit, but the pip installation package does not include this data, so this does not change the size of the package by much.

This pull request replaces https://github.com/awslabs/aws-viewer-for-cbmc/pull/6

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[markrtuttle]

Closing in favor of https://github.com/awslabs/aws-viewer-for-cbmc/pull/57