Changed the setup.py to load development requirements from file.

(Redmine issue: #4216,#3387)

setup.py

@@ -96,13 +96,7 @@ setup(
     #   https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies
     #   https://stackoverflow.com/a/28842733
     extras_require = {
-        'dev': [
-            'nose',
-            'pyflakes',
-            'pylint',
-            'sphinx',
-            'sphinx-rtd-theme'
-        ]
+        'dev': read_requirements('conf/requirements-dev.pip'),
     },
     scripts = [
         'bin/mentat-backup.py',