Generalize continuous check in chain trajectory

[jaclark5]

Fixes #3546

Changes made in this Pull Request:

• Added a CONCEPT for how to fix this issue with a base.ReaderBase method.

Note that the overwritten method in the LAMMPS reader was a solution that was integrated into my personal working version with very ugly if statements. I think a solution like this will keep things clean.

The tests fail and I don't know why, I could use some input.

PR Checklist

• [ ] Tests?
• [ ] Docs?
• [ ] CHANGELOG updated?
• [X] Issue raised/referenced?