Add basic proxy support

Support proxy configuration for proxies that support HTTP tunnel feature.
Only basic authentication is implemented.

SSL handover after CONNECT TCP tunneling, by making sure all
incoming data from proxy is read before moving forward.

Maximum proxy responses are limited to 10MiB. Go over this and the code will ignore anything proxy has to say.

JFRWebSocket.h

@@ -113,6 +113,16 @@
  */
 @property(nonatomic, assign)BOOL selfSignedSSL;
 
+/**
+ SSL security level for connection.
+ See the kCFStreamSocketSecurityLevel constants for accepted values.
+ If left nil (unset) kCFStreamSo cketSecurityLevelNegotiatedSSL is used.
+ 
+ NOTE: On iOS7 (and 8?) kCFStreamSocketSecurityLevelNegotiatedSSL will fail for servers that negotiate SSL level lower than TLSv1
+       Thus it's wise to set this to kCFStreamSocketSecurityLevelTLSv1 in most cases.
+ */
+@property(nonatomic, strong)NSString *securityLevel;
+
 /**
  Use for SSL pinning.
  */