[api] first step to make project status in the webui more reasonable

adding a /webui/project_status route that is taking only the part of the
/status/project route that is interesting for the webui and outputs it
as JSON

To do this I had to refactor quite a big part of code and also optimized
it here and there
[webui] make the project test case as reliable as the package
[backend] bs_srcserver add summing up waiting jobs as well in workerstatus
[api] filter packages by users before doing all the rest
[api] Ancor gave me a great tip: rails 4 has pluck

Just feel the beauty of
-      infos[:incidents] = subprojects.select("projects.name").map { |p| p.name }.sort.uniq
+      infos[:incidents] = subprojects.pluck("projects.name").sort.uniq
[api] fix code api code that is only covered by webui test suite
[api] make even more use of pluck

it e.g. reduces the runtime of /source from 1500ms to 800ms (all that
overhead of creating ruby objects is gone)