TestObjects: introduce name generator for transaction participant groups

[0pdd]

The puzzle 702-afcf43b4 (from #702) in src/test/java/ru/mystamps/web/service/TestObjects.java (lines 214-214) has to be resolved: "TestObjects: introduce name generator for transaction participant groups"

The puzzle was created by Slava Semushin on 03-Dec-17.

Tech debt for: 2da5416 (#702)

[0pdd]

@0pdd the puzzle #926 is still not solved.