Template collection.xconf

[wolfgangmm]

Atm there's only one collection.xconf per profile. Feature profiles may require their own indexes though (e.g. the register profile needs indexes on person and place). Two possible solutions:

1. make sure we can have collection.xconf for particular subcollections of the data collection, which means that post-install.xql would have to copy them to the correct place
2. template the main collection.xconf to include index configuration fragments supplied by feature profiles