add generic List type to API server and use throughout

[krancour]

Follow up to #1808

Starts to make use of generics.

This PR is decomposed into the following commits:

• Add generic list type
• Remove non-generic list types
• Transition all API server code from non-generic list types to the generic list type
• Resolving conflicts that arose after #1903 added new units tests

There are no functional changes in this PR.

Additionally, I've proactively commented in-line on the very, very few changes wherein the reason for them might not be immediately evident without explanation.

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[krancour]

/brig run