Create a /server API for register servers

This allow to push to the controller information about
the connection to a server.

gns3server/controller/__init__.py

@@ -22,6 +22,9 @@ from ..config import Config
 class Controller:
     """The controller manage multiple gns3 servers"""
 
+    def __init__(self):
+        self._servers = {}
+
     def isEnabled(self):
         """
         :returns: True if current instance is the controller
@@ -29,6 +32,19 @@ class Controller:
         """
         return Config.instance().get_section_config("Server").getboolean("controller")
 
+    def addServer(self, server):
+        """
+        Add a server to the dictionnary of servers controlled by GNS3
+        """
+        self._servers[server.id] = server
+
+    @property
+    def servers(self):
+        """
+        :returns: The dictionnary of servers managed by GNS3
+        """
+        return self._servers
+
     @staticmethod
     def instance():
         """