added target entity

api/target/models.py

@@ -0,0 +1,12 @@
+from api.database import (Model, SurrogatePK, db,
+                          Column, reference_col, relationship)
+from sqlalchemy import String
+
+from api.target_exchange.models import TargetExchange
+
+class Target(SurrogatePK, Model):
+    __tablename__ = "target"
+    name = Column(String(255), unique=True, nullable=False)
+    routing_key = Column(String(255), nullable=False)
+    target_exchange_id = reference_col(TargetExchange.__tablename__, nullable=False)
+    exchange = relationship(TargetExchange.__name__, backref=db.backref('targets'))