Add feature argument to the harvest command

* use parser.add_argument() instead of make_option()

* default values for options are already defined in the parser

* verbosity=4 is now not supported anymore (cannot remove arg with argparse)

* do not define requires_system_checks for versions lower than 1.9

* verbosity default is 3

* requires_model_validation is useful for 1.6 and below

* Test on django 1.9, drop python 2.6 support

* update most requirements and fix failing test

As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

* django.db.models.loading.get_models => django.apps.apps.get_models

* requires_model_validation -> requires_system_checks in Django==1.9

* accept list and tupls for LETTUCE_APPS and LETTUCE_AVOID_APPS

* stopserver() function is unused

* leverage LettuceRunnerError and CommandError instead of SystemExit

* ScenarioResult knows about optional outline

* ScenarioResult needs all_steps (outlines...)

* TotalResult.is_success property

* jsonreport_output plugin + command options

* extract background information as well

* make sure step.meta.success/failed are booleans

* add functional tests for the jsonreport plugin

* more precise meta for features (scenarios/steps breakdown)

* track total/feature/scenario/step duration

* fix meta.scenarios.success when there are failures

* take into account skipped/undefined/failures to determine scenario success

New hook for outline added. It works before_each outline and after_each outline. It is required for PyCharm lettuce scenario outline support, and it is useful anyway.

Old hook is left unchanged to keep old API, but it can't be used because it is not called before and after each outline, and in case of exception and fastfail it is called after after_scenario.

Fix japanese

Typo in wtf.html: a adress book -> an adress book

Typo (cli.rst) "some scenarios all feature" add "of"

Update languages.py

cannot assume that dict items are ordered

Use Django 1.7 StaticLiveServerTestCase when available

Ignore all lines with text "Feature:" that do not start with spaces or t...

add make to whitelist_externals since tox does not install it

fix language detection: detect language only in comments

add --root-dir option so discovery does not go up all the way to '/'

docs/conf.py pythonpath fix

⬆ tox 2.1.1

⬆ nose 1.3.7

Add a specific version of lxml to test against

Remove deprecated --use-mirrors option from pip install

Fixes #476, change the syntax of caught exceptions.

Avoid deprecation warning about django's importlib and prepare to django 1.9.

Remove non-ASCII characters from a critical exception's message

⬆ Jinja2 2.8

⬆ cssselect 0.9.1

added compiled regexes