Instead of hard-coded list, invoke hook_reserved_project_names()

My only concern about this going in is that then if a site starts out with only the project and project_release modules, for example, and then someone creates a project called "issues" or "voting", but then later the site wants to also install project_issue and project_voting, there will be problems.

On the flip side, once we start using views the paths that a site might use open up termendously, since things won't be hard coded. So there's the potential that a site that uses non-default paths for the various views might either need to restrict the list of possible projects even further, or may not need to restrict them at all. So having a hook that the site admin could use would be very beneficial.

Maybe we want to add something to hook_requirements that displays a warning if there are collisions between project names and any of the reserved names that come up at a given time from calling this new hook? At least then the site admin could fix things before they got too ugly.

i want to get rid of the reserved name stuff altogether, so i don't like the idea of adding in a hook for it now. i have an issue floating around somewhere for that...

hunmonk's issue is #180316: fix project/mymodule URI insanity.

Re-rolled & committed. Thanks!

This is useful for https://docs.gitlab.com/ee/user/reserved_names.html#reserved-project-names