Fix/wp filter helper options

https://www.openproject.org/work_packages/7472
(see comment #36)

Options can be passed to the path helpers which is necessary for the atom links.

Updated the links on the roadmap view to use the new url helpers.

Wrote some specs.
For the record this is unrelated to this PR. It's happening because the selected user isn't in the list of available users for the filter in the work packages table because they are not in that project anymore.