Add the possibility to set level of validation on events

[t-persson]

Description

Today eiffelib validates all events against the Eiffel JSON schemas and, as such, the eiffellib will never allow any events that do not follow the Eiffel specification.
This can cause some annoyances, especially when updating Eiffel specification versions.

Motivation

The ability to disable validation would end the problems with eiffellib rejecting events on subscribe and publish.

Exemplification

When a very minor update is done to the Eiffel specification, the eiffellib would not reject the events.

Benefits

Easier to just let a program execute and hope that it does not break when new updates to the Eiffel specification come.

Possible Drawbacks

It would allow anyone to just publish and subscribe to any event they want through the eiffellib, even if it's not Eiffel. There is a risk that an internal specification, that does not follow Eiffel, could be created due to having this ability to ignore validation.