Update Umbraco.gitignore

Commented out the rules that rely on 3rd-party packages (Courier, ELMAH, ImageGen, ImageResizing, TeaCommerce and uSync)
Merge branch 'patch-2' of https://github.com/leekelleher/gitignore into leekelleher-patch-2

Conflicts:
	Umbraco.gitignore, resolved.
Merge branch 'origin/leekelleher-patch-2'