Add whitespace linting for all files

[mduan]

Currently, we only have whitespace linting for python files. However, we should enforce whitespace rules for all source files.

Some things to lint for include:

• disallowing tabs
• disallowing trailing whitespace
• enforcing 80-char line length

[divad12]

Enforcing 80-char line length might be tricky since there are some URLs and lines of code that just don't fit in 80 chars.... The rest sounds good.

[jlfwong]

Sensible linters don't complain about lines that are > 80 characters when there's a word longer than 80 characters on that line (our python linters deal with this gracefully)

[divad12]

@phleet Sweet 👍

[mduan]

Looks like JSHint currently doesn't support detecting trailing whitespace on empty lines, and they're removing the ability to check for trailing whitespace in a future release: jshint/jshint#1554. So we'll need to use something else for checking for trailing whitespace in JS files.

[divad12]

Looks like that issue references https://github.com/mdevils/node-jscs