Added 'water.py' solvent component

mbuild/components/solvents/water.py

@@ -0,0 +1,18 @@
+import numpy as np
+
+from mbuild.compound import Compound
+from mbuild.tools.tiled_compound import TiledCompound
+
+
+class Water(Compound):
+    """An SPC water box."""
+    def __init__(self):
+        super(Water, self).__init__()
+
+        self.append_from_file('spc216.pdb',
+                                relative_to_module=self.__module__)
+        self.periodicity = np.array([1.0, 1.0, 1.0])
+
+if __name__ == "__main__":
+    s = Water()
+    s.visualize(show_ports=True)