0022301: [CEA] Problems with study dump in SMESH (PPGP large study)

0022301: [CEA] Problems with study dump in SMESH (PPGP large study)

1) fix CheckObjectPresence() to check presence of not only published
objects but also of e.g. mesh editors etc.
2) Avoid adding empty strings cleared by CheckObjectPresence()
3) Optimize performance of search of myKeepAgrCmdsIDs in commands by
 - using _pyStringFamily
 - preventing addition of Groups to myKeepAgrCmdsIDs