everywhere: use different session cookie names

If the user is hosting the dashboard in the same domain as
their blog (with a nginx suburi, for example), the two session
cookies clash; logging into one service logs you out of the other.
With this patch, both have separate names.

Fixes https://gitlab.com/commento/commento-ce/issues/49

api/commenter_session.go

@@ -4,8 +4,11 @@ import (
 	"time"
 )
 
+// A session is a 3-field entry of a token, a hex, and a creation date. Do
+// not confuse session and token; the token is just an identifying string,
+// while the session contains more information.
 type commenterSession struct {
-	Session      string    `json:"session"`
+	CommenterToken string    `json:"commenterToken"`
 	CommenterHex string    `json:"commenterHex"`
 	CreationDate time.Time `json:"creationDate"`
 }