[backend] break channel if a binary for a package is missing
[webui] do not call into API for every test case

There is no more need to clear the internal API cache
[webui] remove issue models
[webui] switch the default back to transactional fixtures

It's much faster and most test cases don't need the cleanup any longer
[webui] remove some more XML models
[webui] remove link model

It was only used for functionality not used (since we default to branch)
[webui] get rid of XPath Collections
[webui] coverage for sitemap
[webui] some coverage for editing groups
[webui] coverage for invalid group (which was indeed broken :)
[webui] some more group coverage
[ci] push coveralls data right from travis
[api] Require running memcached.

Fixes: https://github.com/openSUSE/open-build-service/issues/454
[backend] update clients count in workerstatus
[backend] speed up code filtered _result query
[backend] do not get info of all packages for _repository buildinfo queries
[dist] fix name of cp437 kernel module, nls_cp437
[webui] port to possibly_empty_ul

This avoids duplicating conditions
[api] rename bs_user_id to user_id in all tables
[api] put the user login in the fixtures instead of the id

Same for roles