tmf: Remove the ITmfEventTableColumns extension point

tmf: Remove the ITmfEventTableColumns extension point

Add a getEventAspects() method in ITmfTrace, which allows trace types
to define which aspects can be relevant for their own events.

This becomes redundant with the ITmfEventTableColumn extension point:
now that we build columns directly from aspects, the TmfEventsEditor
can simply call trace.getEventAspects() instead of reading extension
point data. The trace type is already defined in a core extension point,
so we'll pass the event aspect information through that now.

The combination of careful equals() methods in aspects and the use
of a Set in the TmfEventsEditor will allow "merging" aspects/columns
together, like was already the case.

Change-Id: Ic5b6126a50b1b1fdb4b2d5d23eb6a47a57555594
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/36364
Tested-by: Hudson CI