Add option to skip registration.

[kbestak]

Description of feature

For some platforms (e.g. Lunaphore COMET), the data often comes prestitched. Since this is the main platform we will be using, it will be crucial for us to be able to skip registration in the workflow.
Default functionality should stay as registration = true.

Various changes will need to be made so that input validation still works.
Test data will need to be provided for this case as well and the COMET data mentioned in #59 would be a good starting point.