Fix issue lookup on proposal create view to match the changes to the proposal mixing, and to have a consistent API with other proposal routes (issue is referenced by "issue_id", the proposal by "pk").
Fix issue lookup on proposal create view to match the changes to the proposal mixing, and to have a consistent API with other proposal routes (issue is referenced by "issue_id", the proposal by "pk").

hasadna/OpenCommunity,hasadna/OpenCommunity,nonZero/OpenCommunity,hasadna/OpenCommunity,nonZero/OpenCommunity,yaniv14/OpenCommunity,yaniv14/OpenCommunity,yaniv14/OpenCommunity,yaniv14/OpenCommunity,nonZero/OpenCommunity,hasadna/OpenCommunity,nonZero/OpenCommunity