Restructure '_getMetadataTypes` in annotation-page.js

[bctcvai]

This function was originally written in an inline javascript style where embedded functions vs. member functions were favored for event handlers. Because the data structure of tator has increased, the function itself is quite complex containing a lot of nested logic.

In the case of multi videos, it is invoked multiple times often re-acquiring the same information for each video in a multi feed.

Suggestion is to make use of better coding practices, including:

• Functional decomposition
• Use of await syntax to avoid multiple nested promises.
• Avoiding registration of application critical event handlers as anonymous lambda functions

tator/ui/src/js/annotation/annotation-page.js

Line 938 in c38dd2a

_getMetadataTypes(