Update Tool for Booker 1.21 compatibility

Changes needed to work with the upgraded booker, created as working through checklist.

Probably easier to review code by commit.

If want to test against upgraded booker (possibly more effort than required considering how long it took me to go through each API endpoint) then use a configuration containing:

booker:
  api:
    url: "https://booker-web-staging-new.azurewebsites.net/api/"
    email: "devops+essm@uis.cam.ac.uk"
    password: {same password as live booker - see 1password}

Also may want to restrict timeframe to next term:

termtime:
  timeframe: Custom
  timeframes:
  - c: Custom
    f: 1
    fDate: '2022-01-01'
    l: 52
    lDate: '2022-07-01'
    n: Custom

Clearly mark any test bookings created and cancel them when done.

Closes: administration#46