Refactor settings to make possible override in settings

[yakky]

This refactor the settings to make easy to override by using https://docs.djangoproject.com/en/1.10/topics/testing/tools/#overriding-settings

Trick by Guido Van Rossum himself:

# module foo.py

import sys

class Foo:
    def funct1(self, <args>): <code>
    def funct2(self, <args>): <code>

sys.modules[__name__] = Foo()

See https://mail.python.org/pipermail/python-ideas/2012-May/014969.html

[yakky]

anyone available for a review?

[codecov]

Codecov Report

Merging #72 into master will increase coverage by 0.29%.

@@            Coverage Diff             @@
##           master      #72      +/-   ##
==========================================
+ Coverage    62.4%   62.69%   +0.29%     
==========================================
  Files           7        7              
  Lines         125      126       +1     
  Branches       10       11       +1     
==========================================
+ Hits           78       79       +1     
  Misses         41       41              
  Partials        6        6

Impacted Files	Coverage Δ
robots/settings.py	100% <100%> (ø)	✅

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