Obsoleted methods in old Casing class and redirects to use StringExtensions. Removes eroneous webforms files not needed in the Umbraco.Web prject

(didn't convert the related UI project ones to have code behinds though... one thing at a time and there's a lot of them to do... over time)

src/Umbraco.Core/StringExtensions.cs

@@ -21,6 +21,10 @@ namespace Umbraco.Core
     ///</summary>
     public static class StringExtensions
     {
+
+        public const string UmbracoValidAliasCharacters = "_-abcdefghijklmnopqrstuvwxyz1234567890";
+        public const string UmbracoInvalidFirstCharacters = "01234567890";
+
 		/// <summary>
 		/// Encrypt the string using the MachineKey in medium trust
 		/// </summary>
@@ -830,8 +834,8 @@ namespace Umbraco.Core
         /// <returns>An alias guaranteed not to contain illegal characters</returns>
         public static string ToSafeAlias(this string alias)
         {
-            const string validAliasCharacters = "_-abcdefghijklmnopqrstuvwxyz1234567890";
-            const string invalidFirstCharacters = "01234567890";
+            const string validAliasCharacters = UmbracoValidAliasCharacters;
+            const string invalidFirstCharacters = UmbracoInvalidFirstCharacters;
             var safeString = new StringBuilder();
             int aliasLength = alias.Length;
             for (int i = 0; i < aliasLength; i++)