Closing the PowerShell Integrated Console should not kill the language server

[daviwil]

Currently closing the PowerShell Integrated Console tab will cause the language server to be killed. After doing this, Atom will hang while shutting down due to an issue in atom-languageclient that should be resolved by PR https://github.com/atom/atom-languageclient/pull/169.

I think the standard behavior is that closing the tab will just hide it, not kill the console entirely.