Fix series and groups options merging
Fix series and groups options merging

 * Check whether group is of type AVG or SUM
 * Use group name as series options' key
 * Stop overriding matching groups with source series options

githubert/facette,yonglehou/facette,vovkasm/facette,githubert/facette,iaean/facette,yonglehou/facette,iaean/facette,vovkasm/facette,hirocaster/facette,iaean/facette,githubert/facette,yonglehou/facette,facette/facette,facette/facette,vovkasm/facette,hirocaster/facette,facette/facette,facette/facette,hirocaster/facette