Add Austria network logic

[nvkelso]

We have shield artwork for Austria's roads, but no network values because the data is sparse there so we need to compute values.

• AT:S-road S Schnellstraßen (officially Bundesstraßen S)
• AT:L-road Landesstraße

We already have, from data:

• AT:A-road motorways (even S that are motorways, sigh)