Synchronized webhooks processing.
Reduced webhooks thread pool queue size, in order to reduce number of
needless database queries.
Fixed bug that caused webhooks processing never to end (believe this
would have been triggered when a profile was modified, e.g. by user,
while it was part of the current webhooks batch).
Merge pull request #519 from ORCID/dev-webhooksProcessingAlgorithmTweaks

Webhooks processing algorithm tweaks