chore: testing infrastructure (jasmine+karma+phantomjs)
feat(ranking): ranking service orders a arbitrary array by mapping indices to new positions in its own data structure
refactor(ranking): more generalized ranking service (becomes order service)
feat(ranking): ranking uses the new ordering service
refactor(ranking): the ordering service doesn't need the items at ordering creation but only at rendering -> an ordering is independent of any specific array
refactor(ranking): improved API for the ordering service
refactor(ranking): ordering loaded from firebase
feat(ranking): ranking is saved into firebase