Implement interactive restraint picking

[IAlibay]

Unfortunately these kinds of scenarios can happen...

This is problematic because the lowest RMSD position ends up picking up a rather unfavourable dihedral angle (I'll update if this simulation doesn't fail...).

For cases such as these, it would be useful to implement an interactive mode where the users can limit the sampling selection to a region of interest.

This is going to be rather large thing to implement, it'll probably a need a complete refactoring of the code.