Added initial requirements.txt file for robot libraries

requirements.txt

+###### List of required python libraries ######
+## To install the libraries, use:
+# pip -r requirements.txt
+
+robotframework==3.1
+RESTinstance==1.0.0rc4
+robotframework-dependencylibrary==1.0.0.post1
+robotframework-jsonlibrary==0.3
+robotframework-jsonschemalibrary==1.0