Add icons for Command Explorer

[corbob]

Change refrech icon to use octicons (https://octicons.github.com)

PR Summary

Add some icons for usability.
Add configuration to toggle visibility of Command Explorer
Needing to right click isn't super intuitive.

PR Checklist

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[TylerLeonhardt]

I think the setting just needs a quick name check but LGTM otherwise.

[corbob]

@TylerLeonhardt

From my investigation, if you navigate to View > Appearance there's two options. There's Toggle Side Bar and Hide Activity Bar. If you select Toggle Side Bar it will toggle the view of the green highlighted section. While if you select "Hide Activity Bar" it will toggle the red highlighted section. Based on this behaviour, do you still want to change it to activityBar instead of sideBar? If we don't change it from sideBar, then the description at least should change to be side bar to match the UI.

Reference screenshot:

[TylerLeonhardt]

Given this info. Ignore all my comments. :)

[bergmeister]

There should've been a space after the colon (:). I opened PR #1688 to fix it. Running Invoke-Build at the end helps with that.