Reassign child cats when deleting parent cat (#27)

- Create common page/post edit field template (#25)
- Fix relative URL adjustment throughout
- Fix upload name sanitization regex
- Create modules within Admin handler module
- Enable/disable podcast episode fields on page load
- Fix upload destination casing in templates
- Tweak default theme to show no posts found on index template
- Update Bootstrap to 5.1.3 in default theme

src/MyWebLog/Handlers/User.fs

@@ -51,7 +51,10 @@ let doLogOn : HttpHandler = fun next ctx -> task {
             AuthenticationProperties (IssuedUtc = DateTimeOffset.UtcNow))
         do! data.WebLogUser.SetLastSeen user.Id user.WebLogId
         do! addMessage ctx
-                { UserMessage.success with Message = $"Logged on successfully | Welcome to {ctx.WebLog.Name}!" }
+                { UserMessage.success with
+                    Message = "Log on successful"
+                    Detail  = Some $"Welcome to {ctx.WebLog.Name}!"
+                }
         return!
             match model.ReturnTo with
             | Some url -> redirectTo false url next ctx