[Thermo] Species size defaults to 1.0

This mostly affects surface phases, where a species size of 0 causes
several problems.

include/cantera/thermo/Species.h

@@ -24,7 +24,7 @@ public:
 
     //! Constructor
     Species(const std::string& name, const compositionMap& comp,
-            double charge=0.0, double size=0.0);
+            double charge=0.0, double size=1.0);
 
     Species(const Species& other);
     Species& operator=(const Species& other);

interfaces/cython/cantera/test/test_thermo.py

@@ -638,7 +638,7 @@ class TestSpecies(utilities.CanteraTest):
 
     def test_defaults(self):
         s = ct.Species('H2')
-        self.assertEqual(s.size, 0.0)
+        self.assertEqual(s.size, 1.0)
         self.assertEqual(s.charge, 0.0)
 
     def test_index_accessor(self):

src/thermo/Species.cpp

@@ -10,7 +10,7 @@ namespace Cantera {
 
 Species::Species()
     : charge(0.0)
-    , size(0.0)
+    , size(1.0)
 {
 }