Make dependancy adal optional

Author: iamneha

requirements.txt

@@ -9,4 +9,3 @@ ipaddress>=1.0.17;python_version=="2.7"  # PSF
 websocket-client>=0.32.0,!=0.40.0,!=0.41.*,!=0.42.* # LGPLv2+
 requests # Apache-2.0
 requests-oauthlib # ISC
-adal>=1.0.2 # MIT

setup.py

@@ -27,7 +27,9 @@
 # prerequisite: setuptools
 # http://pypi.python.org/pypi/setuptools
 
-EXTRAS = {}
+EXTRAS = {
+    'adal': ['adal>=1.0.2']
+}
 REQUIRES = []
 with open('requirements.txt') as f:
     for line in f: