New PCT uptake functions

[Robinlovelace]

There are in fact many PCT uptake functions, in the pct R package.
I think we should have the following ones implemented:

• uptake_pct_govtarget_2020()
• uptake_pct_godutch_2020()
• uptake_pct_ebike_2020()
• uptake_pct_govtarget_school2
• uptake_pct_godutch_school2

The "2" signifies more recent versions after we recalibrated the model. Basically, I think we should add those 3 additional functions.

I'm up for giving it a first bash, needed for SchoolRoutes

[Robinlovelace]

Just one more to go (the e-bike one) and may be worth doing some more spot checks compared with R versions so re-opening. See R spot checks in link below..