Add multi-select to context menu commands that most need it

[bwateratmsft]

Fixes #331, fixes #1453.

This PR is similar to #1620 (and also covers what #1494 does) but adds multi-select support to all of the explorer groups (except Registries), with multi-select support for the following commands:

Containers, Images, Networks, Volumes: Remove
Containers only: Start, Stop, Restart

It also will filter off nodes for which the action taken is not eligible (for example, parent nodes, or stopping an already-stopped container). Unfortunately it shows actions for whatever was the specific item in the selection set that was right-clicked (not actions that are valid for all selected items) but we think that for the most part that will not be an issue.

Some of the remaining commands do not make sense as a multi-select (for example, Image > Copy full tag), some of the others maybe make sense but we are leaving them as single-select at this time (for example, Inspect).

[eine]

Some of the remaining commands do not make sense as a multi-select (for example, Image > Copy full tag), some of the others maybe make sense but we are leaving them as single-select at this time (for example, Inspect).

If this is applied, I'd request to please NOT close #331 as part of this PR.

[bwateratmsft]

Some of the remaining commands do not make sense as a multi-select (for example, Image > Copy full tag), some of the others maybe make sense but we are leaving them as single-select at this time (for example, Inspect).

If this is applied, I'd request to please NOT close #331 as part of this PR.

I think it would be appropriate to close #331 but create a new one for Inspect/View Logs/etc.). This would help us gauge the importance of taking such a change.