Address the hardcoded number of commands

[shanereetz]

In several places in the original code, the magic value "19" was referenced as a loop iterator.
It's unclear if this was to limit work done per cycle, or commands that could be in a group.

I moved this to a value into a constant "maxRelatedGroups : USINT := 19; // TODO evaluate this" in PLCOpenCommand.

To address this issue, either more context could be added to the comment noted above, or perhaps the value should be increased, or something else.