Add appdirs dependency for preferences management.

Author: alejandroautalan

setup.py

@@ -157,6 +157,7 @@ def __init__(self, master):
     cmdclass={
         'install': CustomInstall,
     },
+    install_requires=['appdirs>=1.4'],
     classifiers=[
         "Programming Language :: Python",
         "Programming Language :: Python :: 2.7",