Consider requiring more rankings per category before "Finish" unlocks

This is somewhat dependent on what happens with #152.

We reduced the number of required rankings in a category before finishing, but it feels like the adjustment went slightly too far? If you finish a category as soon as possible, nearly half of the projects receive 0 allocation as they may have only come up once or twice against major projects.

consider whether to slightly increase number of rankings before "Finish" is unlocked for more fine tuned allocations.

Especially important if we are considering not changing the way the Finish button works (as outlined in #152). If the new flow is adopted, this may be less of an issue.