Add netbox dcim platform

[tigpas]

After https://github.com/benclaussen/NetboxPS/pull/60

I whould like to add the add/remove/set for DCIM/Platform. I moved Get-NetboxDCIMPlatform.ps1 to the correct folder.

For autogenerating slugs, I created an helper function. If this is accepted, all generating of slugs should be updated

     if (-not $PSBoundParameters.ContainsKey('slug')) {
-        $PSBoundParameters.Add('slug', $name)
+        $PSBoundParameters.Add('slug', $($name | Get-NetboxSlug))
     }