Use most common/popular ref and destination

[freenerd]

Ways can have several ref and destinations. These are usually ; delimited. Currently we are only always using the first one. Instead, we should use the most common or popular one.

As an example, imagine a cross-country road that has the following refs on the way:

• I-80
• I-80;I-81
• I-80;I-81;DETOUR-20
• I-80
• I-90;I-80
• I-90;I-80
• I-80

It would be great if the user would always only get I-80 as the ref.

We could implement this via a pre-processing step where we create a priority list (based on occurence, maybe mixed with length of staying on segments) and when deciding for a ref within a way, we should use the one with highest priority.

[freenerd]

During the pre-processing step, we may also handle mode changes #18 and waypoints #7

[freenerd]

Note that it likely makes sense to have one combined priority list for destinations and ref, since OSRM is mixing the destination:ref tags into the destinations field

[TheMarex]

Cross-linking #115 (comment) here as another test case for this.

[freenerd]

There is a prototypical implementation in #77