Connect and Disconnect cmdlets. Refacoring

Implementation of Connect-ODS and Disconnect-ODS.
Renamed ConnectionInformation to SessionInformation.
Renamed "hostname" variables to "url", because that's what it is.
Introduced error classes.
Made secure and insecure connect possible (PSCredentials or plaintext).
Tests for connecting and disconnecting.
Merge pull request #3 from sburnicki/connect_cmdlet

Connect and Disconnect cmdlets. Refacoring