relax SVN archive

Partial fix for bug #12591 (https://gna.org/bugs/index.php?12591).

This was reported by Chris Brosey (chris dot a dot brosey att vanderbilt dot edu).

If no model is ever selected in the model_selection.select() function, then relax no longer fails.
The failure is however caused by another problem elsewhere within relax, so this fix is not
complete.

Fixes for the system test script rename of the previous commits.

Deleted the old system test script.

Renamed the system test script.

Modified the system test to additionally catch bug #12591 (https://gna.org/bugs/index.php?12591).

Converted some ints to bools.

Fixed the Scientific Python links as identified by Mate Erdelyi.

Fix for bug #12582 (https://gna.org/bugs/index.php?12582).

This was reported by Chris Brosey (chris dot a dot brosey att vanderbilt dot edu).

The problem was that the frq_labels data structure in the SpinContainer was sometimes set to []
rather than the data structure being missing. Now the structure is being tested if it is either
None or [] before being accessed in the model-free return_units() method.

Added a system test for replicating bug #12582.

Added a missing RelaxError import.

This was discovered when trying to replicate bug #12582 (https://gna.org/bugs/index.php?12582)
reported by Chris Brosey (chris dot a dot brosey att vanderbilt dot edu).