The notification manager has been refactored to use the extension
platform module instead of using `extensionizer` directly. The
extension platform API presents a more ergonomic API, and it correctly
handles errors (which the old notification manager did not). Methods
that the extension platform lacked have been added.
It has been updated to use `async/await` instead of callbacks as well,
for readability.
The `triggerUI` function has also been updated to use the extension
platform instead of `extensionizer`.
* Specify type before parameter name
Various JSDoc `@param` entries were specified as `name {type}` rather
than `{type} name`.
A couple of `@return` entries have been given types as well.
* Use JSDoc optional syntax rather than Closure syntax
* Use @returns rather than @return
* Use consistent built-in type capitalization
Primitive types are lower-case, and Object is upper-case.
* Separate param/return description with a dash