Change project when selection changes in Package Console combo box.

Update the view model's default project when the project selected in
the project combo box is changed.
Pash now available in Package Console.
Fix variables being undefined on next command line in Package Console.

Defining a variable by entering the command line:

    $a = "abc"

Then using the variable again would fail since it would be null.

It seems that the default scoping rules for variables in Pash is
different to Microsoft's PowerShell.

Adding a script via:

    Pipeline.Commands.AddScript(command)

In Pash is equivalent to:

    Pipeline.Commands.AddScript(command, useLocalScope: true);

Whilst in Microsoft's PowerShell this is equivalent to:

    Pipeline.Commands.AddScript(command, useLocalScope: false);