Enable GraphHopper's alternative wayfinding methods

[nilsnolde]

Let's evaluate the dev effort for

• round trip
• alternative routes

Ref. https://github.com/graphhopper/graphhopper/blob/master/docs/web/api-doc.md#flexible

Not sure who to assign here. @sfendrich? What do you think? Smth to look forward to in the new year?;)

[rabidllama]

I have started looking into the round trip thing which seems like it could be promising - though some things that need ironing out first. I will split that one out into a separate issue.

[rabidllama]

I will switch assignment of this over to @takb - @sfendrich if you have started looking into things on this already, then we can look at transferring things across

[sfendrich]

That's fine, I haven't started so far.

[TimMcCauley]

@marq24 @takb @rabidllama it might make sense to update our gh-ors fork once this PR is in? What do you think?
graphhopper/graphhopper#1524

[marq24]

@TimMcCauley sounds like a task for me :-)

[TimMcCauley]

@marq24 hehe, I think you will be the fastest ;) however I think we should wait a little until it's merged into gh's master and released - what do you think?