DEV: Create python class for covariate imports (#237)

python/varspark/covariatesource.py

@@ -0,0 +1,11 @@
+import struct
+import pandas as pd
+from typedecorator import params, Nullable
+
+class CovariateSource(object):
+    def __init__(self, _jvm, _vs_api, _jsql, sql, _jcs):
+        self._jcs = _jcs
+        self._jvm = _jvm
+        self._vs_api = _vs_api
+        self._jsql = _jsql
+        self.sql = sql