Allow multiple installed packages action

[Feature proposal]

Similarly to #12 , it would be convenient to select multiple installed packages, right click, and issue a command for all of them. For instance, selecting packages A and B and selecting "Update" would result in `choco upgrade A B`.

(Of course, this might be nonsense to get "Details" for a multiple selection.)

Start by tracing how installed packages are selected and how existing single-package actions invoke Chocolatey commands. Implement multi-selection for applicable actions such as Update, while preserving or defining behavior for actions like Details; confirm that selecting packages A and B produces a command equivalent to `choco upgrade A B`.

Written by the indexing model from the issue text.