CTP 'unused capacity'

[jensdanb]

Calculation of 'unused capacity' should be done per route. Purging of premature "unused" should likewise be done per route.
Then potential inventory = inventory + unused for all routes.

[jensdanb]

This is only a problem when used capacity > potential capacity for a route, which would have zeroed only that route's capacity without "eating up" capacity from the other routes. Not priority for now.