[master] Use replication throttling mechanism in more than one plugin

A replication throttling mechanism has been in place in ReplicateToLocalSE (and also in the derived ReplicateWithAncestors) for some time, but it was not used in ReplicateToRunDestination which is also used for pre-staging (where this throttling is most useful).

Part of the code was moved to PluginUtilities in order to be used by both plugins.

At the same time, SE group resolution was removed from the script plugin utility in order to let TS plugins do it.

Improved comments and logging from several scripts and script executors