implement frontend for user expiry/duration

this will add an optional validity period to users, where their account
will be disabled (or deleted) a specified amount of time after they
created it.

lang/admin/en-us.json

@@ -10,6 +10,7 @@
         "inviteHours": "Hours",
         "inviteMinutes": "Minutes",
         "inviteNumberOfUses": "Number of uses",
+        "inviteDuration": "Invite Duration",
         "warning": "Warning",
         "inviteInfiniteUsesWarning": "invites with infinite uses can be used abusively",
         "inviteSendToEmail": "Send to",
@@ -20,9 +21,12 @@
         "delete": "Delete",
         "name": "Name",
         "date": "Date",
+        "enabled": "Enabled",
+        "userDurationDescription": "A specified amount of time after each signup, jfa-go will delete/disable the account. You can change this behaviour in settings.",
         "lastActiveTime": "Last Active",
         "from": "From",
         "user": "User",
+        "userDuration": "User Duration",
         "aboutProgram": "About",
         "version": "Version",
         "commitNoun": "Commit",

lang/form/en-us.json

@@ -16,7 +16,8 @@
         "successHeader": "Success!",
         "successContinueButton": "Continue",
         "confirmationRequired": "Email confirmation required",
-        "confirmationRequiredMessage": "Please check your email inbox to verify your address."
+        "confirmationRequiredMessage": "Please check your email inbox to verify your address.",
+        "yourAccountIsValidUntil": "Your account will be valid until {date}."
     },
     "notifications": {
         "errorUserExists": "User already exists.",