Add missing translations in customer

Author: Jeroen

app/code/Magento/Customer/i18n/en_US.csv

@@ -536,3 +536,7 @@ Addresses,Addresses
 "Password forgotten","Password forgotten"
 "My Dashboard","My Dashboard"
 "You are signed out","You are signed out"
+"Associate to Website","Associate to Website"
+"Prefix","Prefix"
+"Middle Name/Initial","Middle Name/Initial"
+"Suffix","Suffix"