Change event messages

Changed structure to be inline with Symphony core. Added event messages as for 2.4 core
Extend EventMessages, and tidy codes up
Typo fix
missing comma
Even more events normalisation
Merge pull request #249 from embarknow/integration

Update Events to make use of `EventMessages`
missed a message ID
Merge pull request #251 from embarknow/integration

missed a message ID.

@brendo, as this is a minor fix, I just merged it.
Removed unnecessary SQL queries when checking activation
Merge pull request #256 from g-wilson/integration

Removed unnecessary SQL queries when checking activation
Possbile resolution for #257