[MATLAB] improved the logging system

-hri_load_logfile: fixed a bug that prevented the creation of the
structure fields, when the variable name contains non-alphanumeric
characters.
-hri_load_logfile: fixed a bug that prevented the logfile to be opened.
-The paths for logging and GUI callbacks are now absolute, and made from
the actual file location. This fixes bugs when the MATLAB current
directory is changed.
-hri_comm: the filename pattern can now be changed from the date to a
counter.