Renamed JSON strings and extracted constants

All JSON that refer to some entity use the same name for it.
Extracted all strings to constants.
Renamed constants that refer to change origin to have common naming.

Implementes Trello Card #50 https://trello.com/c/ZQkSvb8U
Merge branch 'eventFormatRename' of github.com:cdmihai/clientRecorder into eventFormatRename