Resolving lint warnings and errors

[gregmuellegger]

This resolves (nearly) all lint errors. For reviewing this PR keep in mind that my intend was always to just fix the warnings and not do any other refactoring. If you see a semantic change in the PR, please report!

All changes that required changing the semantics were proposed as other PRs:

• Fix "from urls import ..." -> "from readthedocs.urls import ..." #1513
• Fix undeclared variable in core.views.random_page #1514
• Remove doc_builder.backends.asciidoc as we do not support AsciiDoc #1516
• Fix missing variable in project.tasks.webhook_notification #1517
• Remove unused projects.utils.github_paginate #1518
• Use Django's builtin Form.add_error instead of custom addError #1519
• Move dnspython and launchpadlib into requirements/pip.txt #1521

These warnings are still left:

Messages
========

core/management/commands/build_files.py
  Line: 46
    pylint: no-value-for-parameter / No value for argument 'commit' in function call (col 16)

doc_builder/backends/__init__.py
  Line: 1
    pylint: cyclic-import / Cyclic import (core.forms -> core.models)

The first one is discussed in #1512

For the second one, I have not idea how to resolve it. The UserProfile.get_form method imports from .forms import UserProfileForm which is surely the cause for the warning, but the actual reported file that this error occurs in is always different for every run of tox -e lint ...

[ericholscher]

Big 👍

[ericholscher]

This feels un-djangoy -- have they suggested doing this now, or is this just to make the linter happy?

[ericholscher]

Also seems there are a bunch of other places where we're doing it and it isn't alerting. Is it special casing Django model's and forms, but not the api stuff?

[gregmuellegger]

The linter complains if python old-style classes are used. Django makes the Meta classes into new style classes automatically since this ticket: https://code.djangoproject.com/ticket/7342

The restframework however does not. So that's why we made them new-styles classes here by hand. I think of it as "future-proofing" as all classes will be new style classes in Python 3, so we do some testing in that regard here if we make the switch now.

[ericholscher]

We: the circular import, do we actually use the get_form method on the UserProfileForm?

https://github.com/rtfd/readthedocs.org/blob/master/readthedocs/core/models.py#L29-L31 is the issue, but yea, it doesn't break prod, so I'm not sure what the best course of action is.

[ericholscher]

We could do a janky string-based import, but that's just working around the linter, not changing the logic. Perhaps we can just silence the linter?

[ericholscher]

Gonna merge this, but curious about the Meta stuff -- this will rot quickly, so want to get it in.