add enhanced services and add ons to contract

[louking]

• [x] update addons table to allow unit pricing
• [ ] which services is each addon available to?
• [ ] agreement vs invoice
• [x] basic [currently 'finish line']
• [x] course marking [current]
• [x] scoring [add on to basic -- or standalone service]
• [x] chip
• [x] additional distance [add on, current]
• [x] additional chips [add on, per bib over 200]
• [x] video results [add on to scoring, chip]
• [ ] raceday checkin [add on to scoring, chip]
• [ ] FSRC provided bibs [per bib]
• [ ] stand-alone course marking [do we want/need this?]
• [ ] create sql file to upload these changes
• [ ] update documentation