need better solution for uri prefixes

[balmas]

I'm still not entirely happy with the way the uri-prefixes are working, and at some point would like to sort this out. I think the code may be configurable enough at this point, and we just need to mint a stable URI prefix under http://data.perseus.org that we want to use, at which point we would replace all references to "http://www.perseids.org/jackson" with the new prefix and use url rewriting on the data.perseus.org domain to redirect to the appropriate jackson installation. (But we need a strategy that works for testing a new release on a different server too, so this might require some additional thought). Up until now all CITE collections have been under http://data.perseus.org/collections but the image stuff is now sufficiently different from the rest of the CITE implementations that it is probably best to use a different path.