JavaScript commons library

What did you accomplish?

Avoid fetching dereferenced segments in server-side by iterating FF (and RBS) definitions on each update to compute the current set of used segments. CONS: requires iterating all FFs and RBSegment definitions per segmentChangesUpdater call.

Other approaches:

• Previous one: keep track of used segments, adding them to a set. CONS: we cannot know what segments are dereferenced.
• Track used segment counts, as we do with traffic types. CONS: more complex and keys required for Redis/Pluggable

How do we test the changes introduced in this PR?

Extra Notes

Possible approaches: