Fixed issue #14 in v4 branch.

Note
I 'reused' ISiteMapNode.HttpMethod property because it seems to replicate DefaultSiteMapProvider.RouteMethod property (that was used to in the fix in the old project) and it is neither documented nor used after setting it in an ISiteMapBuilder.
Normalized conventions used in #178 to be consistent with the rest of the project.
Merge branch 'v4' of github.com:NightOwl888/MvcSiteMapProvider into v4
Removed unnecessary strategy registrations and comment that was causing havoc in SimpleInjector module.
Fixed issue with #178 and #14 fix because it wouldn't compile under .NET 3.5.
Fixes #179, throw sensible error message if more than one MvcSiteMapNodeAttribute is defined without a parent key.
Added Demo compilation symbol and exclusion logic to the DIConfig.cs file so simply changing the appSettings value MvcSiteMapProvider_UseExternalDIContainer to false will make the MvcMusicStore use the internal DI container. Previously, it required commenting the webactivator line to work.
Fixes #180, 404 error not shown on unknown route with internal DI container.
Moved SecurityTrimmingEnabled and EnableSecurityTrimming settings to the SiteMap constructor so they can be provided at the right multiplicity level.