Windows Installer

**Do not merge**

Fix #419 

This is not ready to merge yet, but I wanted to move the discussion to the code changes from the issue.

I have split the installer into two installers, one **NUnit.Tools** and the second **NUnit.Framework**. 

Tools always installs the latest version and currently includes the engine and the console runner.

Framework installs side by side into a versioned subdirectory. When both installer are installed, it currently looks like this.

```
Program Files (x86)
    NUnit.org
        tools
            engine and console files (1)
        framework
            v3.0.xxx.xxx
                net-2.0
                    nunit.framework.dll
                    nunit.framework.xml
                    nunitlite.dll
                net-3.5 etc...
```

(1) The engine and console are currently in the same directory even though they are two features in the installer. I will move these into engine and console directories once the engine can register itself and be found elsewhere.

## Todo ##

- Add an icon for the install
- Brand the install dialogs with icon and graphics
- Add the assemblies to the registry so they can be referenced.
- Add msbuild targets to nunit.proj

Link is no longer used - use nunit-discuss link