Add more PICA libraries, Covers for PICA

I started adding PICA libraries from this list http://uri.gbv.de/database/opac, going through from the top until Ostfalia Hochschule.
They all have SRU, too, but when we use the PICA API we can also have account support.
Of course, I couldn't test account support. I deactivated it on some libraries, because the login page looked very different and probably doesn't work with the current PICA implementation.
I also moved the ISBN functions I previously added to SRU to a separate class and also used them in PICA to load covers from Amazon using the ISBN, which works in some libraries. Some others put additional info in the ISBN field (the price of the book, for example :) ), that i didn't manage to filter out.