Support for Waltti regions

[ZeiP]

Edit: I changed the PR to cover a more thorough refactoring of the region system and to add all Waltti regions.

This adds support for Hämeenlinna addresses (search range) and uses the Waltti Digitransit API.

Using the same API we can access also the following just by changing the search range:

• Joensuu
• Jyväskylä
• Kajaani
• Kotka
• Kouvola
• Kuopio
• Lahti
• Lappeenranta
• Mikkeli
• Oulu
• Rovaniemi
• Salo
• Vaasa

Additionally Digitransit has the Finland API, which covers all of them, so it might be useful to additionally have one region option that doesn't restrict the address search at all.

Do you have some plans / insight on what should be done to add the rest of the locations to the application?

[hsarkanen]

Squashed to one commit and merged 9556da827f5754ba0799c1b409aad5b88f030d00