Faster adding of new images from Reddit

[nielsmaerten]

Current behavior:

• Top posts are fetched from Reddit
• Masterlist is fetched from Firebase
• Function iterates over the posts, and each post that's not in the Masterlist is added to Firebase

Needless to say, this is not efficient...

Suggested behavior:

• Posts are fetched from Reddit
• All posts are sent to Firebase using a batch update call

This would result in a null operation for posts that are already in the Masterlist, it's the same data, so nothing changes.
For posts that are not already in there, this will result in new nodes being created.
Triggering in turn the onNewMasterImage function, which will fill in the remaining details.