Feat update group

[ccampanale]

Supersedes and closes #34. I wanted to refactor several core functions from promises to async/await style in order to also consolidate some of the code. Since there were overlapping changes in both of my feature branches, I decided to merge the changes for #33 into those for this new PR.

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Implements #33.

• adds configuration contribution to extension
• adds configuration class to extension to manage configuration access and update
• updates the editor group tree data provider minimize() method to optionally prompt for a group name if enabled in configuration

Implements possible solution for #20

• adds new command contribution to extension for "update minimized group" functionality with enablement based on the number of minimized groups being greater than 0
• adds new title menu contribution pointing to new update command
• adds context item and update logic to support new command enablement
• updates minimize() function to be optionally called with new update: boolean parameter in signature which will prompt for the group to update

Please let me know if there are any questions/concerns.