Set default day exceptions to empty string for cloned course.
Set default day exceptions to empty string for cloned course.

Resolves #400

KarmaHater/WikiEduDashboard,alpha721/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,majakomel/WikiEduDashboard,Wowu/WikiEduDashboard,alpha721/WikiEduDashboard,Wowu/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WinnySilva/WikiEduDashboard,majakomel/WikiEduDashboard,ragesoss/WikiEduDashboard,alpha721/WikiEduDashboard,KarmaHater/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,MusikAnimal/WikiEduDashboard,sejalkhatri/WikiEduDashboard,Wowu/WikiEduDashboard,alpha721/WikiEduDashboard,feelfreelinux/WikiEduDashboard,feelfreelinux/WikiEduDashboard,WinnySilva/WikiEduDashboard,sejalkhatri/WikiEduDashboard,Wowu/WikiEduDashboard,adamwight/WikiEduDashboard,KarmaHater/WikiEduDashboard,sejalkhatri/WikiEduDashboard,majakomel/WikiEduDashboard,ragesoss/WikiEduDashboard,sejalkhatri/WikiEduDashboard,MusikAnimal/WikiEduDashboard,KarmaHater/WikiEduDashboard,adamwight/WikiEduDashboard,feelfreelinux/WikiEduDashboard,majakomel/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,feelfreelinux/WikiEduDashboard,MusikAnimal/WikiEduDashboard,sejalkhatri/WikiEduDashboard,adamwight/WikiEduDashboard,WinnySilva/WikiEduDashboard,MusikAnimal/WikiEduDashboard,ragesoss/WikiEduDashboard