V4

Fix for issue #14 (Use GET to determine node accessibility) for the v4 branch.

Replicates pull request #74 for the v4 branch.

### Important
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 I did not find neither documentation nor usages after it is set in an ISiteMapBuilder.

I also had to modify AuthorizeAttributeAclModule protected interface and IMvcContextFactory public interface.

Please review the changes and tell me if HttpMethod can be used this way or I should introduce a new attribute.