lttng: Add interface to abstract the event layout away

lttng: Add interface to abstract the event layout away

It would be possible to run the kernel analyses using events coming
from different tracers (or different versions of the same tracer).
This adds a IKernelAnalysisEventLayout, which specifies know concepts
in the Linux kernel, and the "support implementation" of each tracer
(or version) can extend it.

This will allow re-using the same modules and state providers, no matter
which actual tracer took the kernel trace. Also avoids having to define
separate trace types.

Also took the chance to rename some classes and packages to align them
better (i.e., the "CPU usage" and "kernel" analyses now use the same
naming scheme).

Change-Id: I0f073060071991e206011810bbb50dd826c688a8
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/36185
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>