Move traceable app. data to a seperate C file

Move traceable app. data to a seperate C file

All traceable application data structure and functions
are now in traceable-app.c/.h.

To remove traceable app data struct dependency from main.c,
register_traceable_app, unregister_traceable_app and get_app_count
is added. Also, main.c is now using these function.

Also, the find_app_by_pid returns the struct pointer.

Minor spaces fix in the code for session.c/.h and main.c

Signed-off-by: David Goulet <david.goulet@polymtl.ca>