Fix: add LTTngEvent class to fix delayed logger

Fix: add LTTngEvent class to fix delayed logger

This commit introduces a new object called LTTngEvent that represent a
LTTng event containing some attributes, for now loglevel data.

Instead of moving event string name around, this object is created once
and kept in the log handler so once a record is publish we can match
attributes such as loglevels.

This has to be done in order to fix the issue where we have a Logger
that appears later on during runtime (with the timer that poll every 5
seconds). With a created event object we can lookup back the event
attributes and enabled it accordingly. Same goes with the * (all events)
where we now keep the loglevel values process wide so we can force the
new events to use it.

Signed-off-by: David Goulet <dgoulet@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>