Implement email template generation

Variables are surrounded by {}, and initial (default) templates are
generated on demand from the plaintext version of emails. The custom
emails are intended to only be used if the user actually changes them,
as they lose the features of the default ones, such as tables.

lang/email/en-us.json

@@ -7,18 +7,21 @@
         "helloUser": "Hi {username},"
     },
     "userCreated": {
+        "name": "User creation",
         "title": "Notice: User created",
         "aUserWasCreated": "A user was created using code {code}.",
         "time": "Time",
         "notificationNotice": "Note: Notification emails can be toggled on the admin dashboard."
     },
     "inviteExpiry": {
+        "name": "Invite expiry",
         "title": "Notice: Invite expired",
         "inviteExpired": "Invite expired.",
         "expiredAt": "Code {code} expired at {time}.",
         "notificationNotice": "Note: Notification emails can be toggled on the admin dashboard."
     },
     "passwordReset": {
+        "name": "Password reset",
         "title": "Password reset requested - Jellyfin",
         "someoneHasRequestedReset": "Someone has recently requested a password reset on Jellyfin.",
         "ifItWasYou": "If this was you, enter the pin below into the prompt.",
@@ -26,11 +29,13 @@
         "pin": "PIN"
     },
     "userDeleted": {
+        "name": "User deletion",
         "title": "Your account was deleted - Jellyfin",
         "yourAccountWasDeleted": "Your Jellyfin account was deleted.",
         "reason": "Reason"
     },
     "inviteEmail": {
+        "name": "Invite email",
         "title": "Invite - Jellyfin",
         "hello": "Hi",
         "youHaveBeenInvited": "You've been invited to Jellyfin.",
@@ -39,12 +44,14 @@
         "linkButton": "Setup your account"
     },
     "welcomeEmail": {
+        "name": "Welcome email",
         "title": "Welcome to Jellyfin",
         "welcome": "Welcome to Jellyfin!",
         "youCanLoginWith": "You can login with the details below",
         "jellyfinURL": "URL"
     },
     "emailConfirmation": {
+        "name": "Confirmation email",
         "title": "Confirm your email - Jellyfin",
         "clickBelow": "Click the link below to confirm your email address and start using Jellyfin.",
         "confirmEmail": "Confirm Email"