Second part refactor of webservices

[Thiago Macieira]

This patch series continues the refactoring of the zip-creation code
that I started for 4.0. While for 4.0 they were just bugfixes, this is
now pure refactoring and makes the code more C++-like. Sorry, Lubomir...

An added benefit is that this now creates proper, translated error
messages about the zip-file creation. I didn't translate the error
messages that I thought would only happen in internal error cases,
though.

The last patch is purely cosmetic and could be skipped if the
maintainers disagree on what is more readable.