Add `uncertain` data for Demoskop polls

Source: http://www.demoskop.se/wp-content/uploads/2014/12/Väljarbarometer-Över-tid-1998-Dec-2014.pdf
Add `uncertain` for Ipsos 2012-11-30 poll

Source: http://ipsos.se/sites/default/files/webfm/valjarbarometern-2012-11.pdf
Add uncertain for 2014-09-19 Novus poll

Source: http://novus.se/vaeljaropinionen/tv4novus-vaeljarbarometer/2014/tv4novus-vaeljarbarometer-10-september-2014-skillnanden-mellan-blocken-minskar-ytterligare.aspx
Add `uncertain` for SCB polls

Source: http://www.statistikdatabasen.scb.se/pxweb/sv/ssd/START__ME__ME0201__ME0201A/Rostningssympati190/?rxid=518c949d-1a20-4151-ba33-258d6e42129e
Add (and fix) `uncertain` data for United Minds

Source: http://www.unitedminds.se/sites/unitedminds.se/files/attachment/UnitedMinds_Aftonbladet%20Väljarbarometer%20rapport%20del%203%20sept%202014.pdf
Merge pull request #23 from urdh/missing-uncertain

Add missing `Uncertain`data