Issue/7 json complete mode

[bogdanadrianmarc]

This PR addresses issue #7 by adding support for the complete JSON mode. The issue is that PPD uses JSON compact mode and UKHPI uses JSON complete mode, and currently the latter is not supported; this PR adds that. The repo with the new SAPINT API for LR is here: https://github.com/epimorphics/lr-data-api (I'm using the master branch). From my tests with the LR apps nothing broke by adding this and UKHPI actually works now, but please run this to double check.

@ijdickinson's suggestions from last PR did not carry over, but I will address them here in a moment

[ijdickinson]

On the whole I approve of these changes, 👍

I'm still not happy about the design of json_mode_complete though. I've put in the comment some suggestions for changing the implementation of that method to something that is cleaner and more maintainable. There is another approach though, which would be to do some investigation to see how many changes would need to be made to UKHPI for it to use compact mode rather than complete mode. I have no idea off the top of my head, but it may be that the amount of work you need to do to robustly support both compact and complete modes is more than just adapting the app to use the same mode as PPD, and that would make the code more maintainable in the long run. Worth a short investigation, I would think.