Loop-step

* The directory name widget was not displayed for loops over systems in the database.
This is now corrected.

* In a loop "For rows in table" a crietrion on the value of a row might cause an
error due to mismatch of the types. This is now corrected.

2024.11.18: Removed automatic output of structures.
* While often convenient, writing out the structure at the end of the loop was not a
reasonable default. If you want the structure, add a write_structure step in the
loop.

* Added methods in the loop_step module to break from a loop, break_loop(), continue
a loop, continue_loop(), and totally skip an iteration, removing any files
associated with it, skip_iteration.

* When printing the description of the substeps in the loop, the code incorrectly
wrapped the text, which caused issues with e.g. tables.

* For integer loops, ensure that the loop variable is an integer and
make the directory name be value of the loop variable to make it easier
to find the iteration of interest.

* There was a bug selecting system by name in the For Systems in Database branch.