Added ability to look in AppSettings for n2.logout.url and process this during the logout from the management interface.
Resolves https://github.com/n2cms/n2cms/pull/87

Merge commit 'aa41fa6c3b002130bb58256ddcb9f3e3bb698976' into n2cms-2.5

Conflicts:
	src/Mvc/MvcTemplates/N2/Login.aspx.cs