PEP8: run travis checks

- Use a subset of PEP8 checks like in Toolkit
- Add make pep8
- Add pep8 checks to travis
PEP8: W601 .has_key() is deprecated, use 'in'
PEP8: E261 at least two spaces before inline comment
PEP8: E262 inline comment should start with '# '
PEP8: E271 multiple spaces after keyword
PEP8: W293 blank line contains whitespace
PEP8: E203 whitespace before ','
PEP8: E231 missing whitespace after ','
PEP8: E225 missing whitespace around operator
PEP8: E251 unexpected spaces around keyword / parameter equals
PEP8: turn E251 on by default for travis
travis: already prints Python version info
Revert "Fix adding tags"

This reverts commit aa04852e9b9c6a88f4c68c5b9d7502fde1b7b8cc.

Next commit will fix it in a less hacky way.
Unbreak AJAX views using @get_path_obj

Many of our AJAX requests do not have a ‘path’, but @get_path_obj now
requires one always which breaks any views that use it, so relax this
and use the ‘path’ only when present.