Enable multiple threads for events

Currently the Event Rules run with a single thread, meaning that if 2 files arrive at the same time, the event rule must complete the handling of the first file before starting the event rule for the second file.

On my system, the processing of a large file can take over 30 minutes...

I propose enabling multi thread event handling with the use of a setting of perhaps 1 to 10. 1 meaning single threaded (and the default setting), and the subsequent numbers being the maximum event threads running at a time.

This would allow users to find the number of threads that suit their system. For example I think that my system would run happily with 4 threads, based on the overhead of a single thread.