PEP8 compliance

[tgamblin]

Ok y'all, I've finally gone through all the code and PEP8-ified the spack core and the packages. This is important so that the checks we do on PRs are meaningful, and so that it's easy to contribute compliant code without having to fix others' issues.

I added a few exceptions:

• Visual indents (which seem hard to fix and don't add much to the code in the situations I've encountered)
• The checker script makes exceptions for URLs and file paths exceptions a bit more aggressively now.
• Factor out the various json schemas from config.py into their own modules, which should make the code easier to manage.

See what you think before this goes in.
@adamjstewart @davydden @alalazo @robertdfrench @becker33

[robertdfrench]

A+++ would merge again.