added Extra field for fingerprint to be able to save extra data

fingerprint.go

@@ -25,6 +25,7 @@ type Fingerprint struct {
 	Bot           bool                   `bson:"bot" json:"b" form:"b"`
 	ASN           *asndb.ASN             `bson:"asn" json:"asn" form:"asn"`
 	Country       string                 `bson:"country" json:"country" form:"country"`
+	Extra         map[string]string      `bson:"extra" json:"extra" form:"extra"`
 	//UserAgent           string        `bson:"user_agent" json:"user_agent" form:"user_agent"`
 	//Adblock             bool          `bson:"adblock" json:"adblock" form:"adblock"`
 	//AvailableResolution []int         `bson:"available_resolution" json:"available_resolution" form:"available_resolution"`