Only open link in browser when clicked: Closes #5472.
Only open link in browser when clicked: Closes #5472.

WebKit supports the following navigation reasons:

    LINK_CLICKED
    FORM_SUBMITTED
    BACK_FORWARD
    RELOAD
    FORM_RESUBMITTED
    OTHER

We only want to open a link in the browser when navigation is requested
for the "LINK_CLICKED" reason. When an iframe is embedded in an email,
it uses the "OTHER" reason.

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