rewrote CommandExecutor as abstract class with template methods
removed callback using CommandExecutor
updated CommandExecutorTest to reflect API changes
updated eventCommandMap to reflect API changes in CommandExecutor and CommandMappingList
WIP command executor with linked list
consolidated separate commandmapping list and iterator
moved removal of once command to before running hooks
renamed ICommandMappingList to ICommandMappingCollection
added MessageCommandExecutor to messageCommandMap