Auto-export should export blueprints

Currently, the blueprints in the HST configuration are not exported automatically. Yet in a multi-channel project, the blueprints will probably be edited a lot (e.g. to develop a subsite blueprint). Developing blueprints will all require the old laborious cycle using manual XML export etc.

Everything below /hst:hst/hst:blueprints should therefore be exported automatically too, in the structure used in the archetype.