V14: Rename new projects (#15836)

* Rename Web.UI.New back to Web.UI

* Delete new backoffiec folder

* Rename client project

* Add new submodule

* Update template csproj

* Remove more mentions of new

* Add missing views

* Moving up the "Umbraco.Web.UI" proj reference, so that it is the first project listed in solution file (.sln) since it will be selected as startup one in VS by default.

* don't include grid

* Update with section of how to get started with backoffice

* Update .github/BUILD.md

Co-authored-by: Elitsa Marinovska <21998037+elit0451@users.noreply.github.com>

* Add line about white page

---------

Co-authored-by: Elitsa <elm@umbraco.dk>
Co-authored-by: Elitsa Marinovska <21998037+elit0451@users.noreply.github.com>

tests/Umbraco.Tests.Integration/DependencyInjection/UmbracoBuilderExtensions.cs

@@ -120,7 +120,7 @@ public static class UmbracoBuilderExtensions
 
                 var currFolder = new DirectoryInfo(srcFolder);
 
-                var uiProject = currFolder.GetDirectories("Umbraco.Web.UI.New", SearchOption.TopDirectoryOnly).First();
+                var uiProject = currFolder.GetDirectories("Umbraco.Web.UI", SearchOption.TopDirectoryOnly).First();
                 var mainLangFolder = new DirectoryInfo(Path.Combine(uiProject.FullName, globalSettings.Value.UmbracoPath.TrimStart("~/"), "config", "lang"));
 
                 return new LocalizedTextServiceFileSources(