invalid treatment of routeDistribution input

[namdre]

if input vehicles/flows reference a routeDistribution they should be assigned a route sampled from that distribution.
Instead the first route in the distribution gets a strong (~98%) bias.

[namdre]

whenever a route is loaded with external id, a route copy is made and this copy get's its probability reset to 1 (and maybe lowered a bit by the routecostcalculator)
The probability later isn't normalized which causes the sampler to sample it with high probablity