Having thread pool as its own singleton in the library meant that each
kiface had its own threadpool, leading to many multiples of the threads
being started. Placing a singleton class in PGM_BASE ensures that all
kifaces use the same thread pool.
The singleton class can be extended to provide single instance
guarantee for any element across kifaces
Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
