Add systembolaget as input

Add data from systembolagets API.

http://www.systembolaget.se/api/

Products can be found here: http://www.systembolaget.se/api/assortment/products/xml
List of stores can be found here: http://www.systembolaget.se/api/assortment/stores/xml
Which beer are in stock on each store (not amount, only if it is available or not): http://www.systembolaget.se/api/assortment/stock/xml
