Easier building otp-data-con for other, not-hsl digitransits

[robbi5]

hey,

thanks again for building and maintaining the whole digitransit-stack <3

in the last few months, more digitransit instances popped up - I'm maintaining two and currently building a third one.
For using the opentripplanner-data-container I always had to fork the repo and make modifications to add the new router (this is as designed), but I've also always had to make modifications to the Seed step (initialization doesn't work if image doesn't exists), the gulpfile (to add the new router to other mentions of hsl, waltti, finland), the routing check url in test.sh and at other places.

If its okay, I'll going to submit pull requests that keep the functionality, but make it more adaptable for new routers - so adding a new one is only providing router-xyz files and an entry in config.js :)

[optionsome]

Sorry forgot to reply to this issue when I merged the PR but feel free to create more pull requests. Our testing of this project is limited to that our use case somewhat works so there are probably many issues when one tries to use some other data and configuration.