web: add package prefix to package urls

Previously the get parameter cat= was used to list all packages within a debian prefix (e.g. all packages starting with "libg" or "g"). These get parameter leads to a unclean directory structure that is also harder to cache. Instead, we can use paths similar to the debian pool directory layout (e.g. package/libf/libfoo/).

This change refactors the URLs under the package and binary endpoint to always include the prefix. The tests are updated accordingly.

Signed-off-by: Felix Moessbauer felix.moessbauer@siemens.com