added Coalition class

will be used in rPATL formulas

src/storm/logic/Coalition.cpp

@@ -0,0 +1,23 @@
+#include "storm/logic/Coalition.h"
+
+namespace storm {
+    namespace logic {
+
+        Coalition::Coalition(std::vector<std::string> const& playerNames,
+                             std::vector<uint_fast32_t> const& playerIds) : playerNames(playerNames), playerIds(playerIds) {
+            // Intentionally left empty.
+        }
+
+        std::ostream& operator<<(std::ostream& stream, Coalition const& coalition) {
+            stream << "<<";
+            for (auto const& playerName : coalition.playerNames) {
+                stream << playerName << ", ";
+            }
+            for (auto const& playerId : coalition.playerIds) {
+                stream << playerId << ", ";
+            }
+            stream << ">>";
+            return stream;
+        }
+    }
+}