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/Upload.fs

@@ -85,7 +85,7 @@ open System.Text.RegularExpressions
 open MyWebLog.ViewModels
 
 /// Turn a string into a lowercase URL-safe slug
-let makeSlug it = ((Regex """\s+""").Replace ((Regex "[^A-z0-9 ]").Replace (it, ""), "-")).ToLowerInvariant ()
+let makeSlug it = ((Regex """\s+""").Replace ((Regex "[^A-z0-9 -]").Replace (it, ""), "-")).ToLowerInvariant ()
 
 // GET /admin/uploads
 let list : HttpHandler = requireAccess Author >=> fun next ctx -> task {