SVEA-32: Added client country option for paymentplan

In order to update paymentplans in the database we need to know in which
country the client has signed its contract. Added a setting in admin
where the client can choose in which country he/she has signed up with
SVEA.
SVEA-32: Translated 'Your monthly cost'
SVEA-32: Checking for client country
SVEA-32: Removed NL from valid client countries

According to comment by Anneli Halldn:

Vi erbjuder delbetalning för privatpersoner i Sverige, Norge, Danmark,
Finland.
merge master
Merge pull request #99 from madepeople/master

SVEA-32