Check code with gjslint, jshint and flake8
Set unknowDefines to off

This is to avoid this compile error:
info ProjectSample Parsing dependencies
info ProjectSample Compiling 338 sources
ERR! compile ERROR - unknown @define variable goog.json.USE_NATIVE_JSON
ERR! compile
ERR! compile
ERR! compile 1 error(s), 0 warning(s),
ERR! compile 97.6
ERR! compile % typed
Rebuild ProjectSample
Check pyramid_closure code with flake8
Use # noqa in tests
Fix the closure-tools target
Update closure source.py
Merge pull request #1 from camptocamp/linters

Use flake8, gjslint and jshint