Add support for picking the PyLama linter over flake8

[insertjokehere]

This simply adds an option to pick if you want to use flake8 or pylama to run linting on the project

I've kept the changes caused by ci/bootstrap.py in a separate commit, not sure if these changes are actually what you want

[ionelmc]

I've trimmed the envs a bit so it don't blow up over travis' 200 env limit.

[ionelmc]

It's in master now (17f16b0) - seems github ain't smart enough to detect the rebase. Thanks!