Be explicit on the dependencies of comp/main

Previously there was a dependency cycle.
Parameterise the milestone by year
Use a YAML integer for absolute ticket references
Add the venue booking ticket
Add knockout planning
Add a verification script
Add insurance coverage
Add sound tickets
Add in risk assessment updating
Add media consent tickets
Format the Trac descriptions more nicely
Add component validity checking
Remove dependency on ticket 11
Remove trailing whitespace from descriptions
Add a script for creating new subtrees
Add pits setup tickets
Add the kit handback ticket
Add blue shirt order
Add scoring and score entry tickets
Add overall power provision ticket