Use GMime API instead of manually reffering a File: Closes #5467.
Use GMime API instead of manually reffering a File: Closes #5467.

AtticHacker/geary,emersion/geary,mjog/geary,kyoushuu/geary,didrocks/geary,mpdeimos/geary,martinra/geary,mjog/geary,tshikaboom/geary,kpiwko/geary,githubnemo/geary,jimbonator/geary,mjog/geary,robol/geary,githubnemo/geary,rschroll/geary,robol/geary,orlandosanchez/geary,MohamedIM/geary-unofficial,dominickm/Geary,jimbonator/geary,tshikaboom/geary,emersion/geary,robol/geary,glebihan/geary,githubnemo/geary,tshikaboom/geary,martinra/geary,glebihan/geary,aatishnn/geary,aatishnn/geary,dominickm/Geary,orlandosanchez/geary,emersion/geary,geekvigilante/geary,orlandosanchez/geary,AtticHacker/geary,rschroll/geary,glebihan/geary,AtticHacker/geary,kyoushuu/geary,abn/geary,jimbonator/geary,martinra/geary,aatishnn/geary