Particle and Track WG 2019 work plan

A) performance tests and improvements (1)/(2)
 - working with corresponding WGs
B) improvements of code readability and documentation (1)/(2)
C) improvements and update of G4IonTable/G4ParticleTable to cope with muonic atom and hyperons
D) reconsidering production thresholds (1)/(2)
 - working with corresponding WGs

(1) - June 2019
(2) - December 2019