Change configuration file and trace output dir

The configuration file containing the session name information is now at
the HOME location and named ".lttngrc".

The trace output directory is now at the HOME location and named
"lttng-traces" containing the traces of each sessions identified by the
top level directory called "session_name-date-time".

Also fix the metadata's path that was pointing to the old default path
in /tmp/lttng.

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