IIS Application and Virtual Directories, and web site improvements

Two new templates:

 - [x] **IIS Application - Create** - create/update an IIS web application under a web site
 - [x] **IIS Virtual Directory - Create** - create/update an IIS virtual directory under a web site

Both of these can create apps/vdirs under nested paths - e.g., `Default Web Site/apps/myapp`

Also:

 - [x] Minor changes to **IIS Website - Create**, firstly so that it updates the site if it already exists (rather than throwing), and secondly to fix a couple of validation issues.

Ready to merge.