Untested code for IRRDB prefix updates

This alternative uses arrays rather than DB requests to do the heavy lifting.

Untested, written while watching presentations...
[BF] record debug option
Update foreign refs
[IM] Complete yesterday's optimisation work
[IM] Remove database method of prefix updates.

With the database doing the heavy lifting from a blank database:

Database time  : 20.271860837936
Processing time: 0.94397568702698
Network time   : 83.258119821548

and on an update run:

Database time  : 11.44893693924
Processing time: 1.1716868877411
Network time   : 82.974792003632

And with the script doing the heavy lifting from a blank database:

Database time  : 11.148242950439
Processing time: 1.0650501251221
Network time   : 81.734930992126

and on an update run:

Database time  : 1.7090458869934
Processing time: 0.10312080383301
Network time   : 85.016879796982

Thus, the database version is now confined to Git history ;)

I'm all about optimisation and performance. But even I must remind myself sometimes of the cost of a database query :/
Merge branch 'nf-irrdb-playground'