po: Fix a couple of typography issues in the Finnish translation.

[Lauri Kenttä]

"Avankuvan väli:" has this colon on purpose. It's the best way to make 
this translation meaningful in the context (Avainkuvan väli: [BOX] 
kuvaa). I've already discussed this with you in private. My opinion is 
that the original text should be in one piece or at least have a msgctxt 
to allow better translations.

-- 
Lauri Kenttä