Fix loading js and css from collections
Fix loading js and css from collections

Calling add() lose information on

- CSS: $group
- JS: $loading, $group

joeyhenricks/a-broke-vegan,userfrosting/learn,ccardinaux/grav-test,userfrosting/learn,Sommerregen/grav,JamesPan/gravbox,JamesPan/gravbox,Vivalldi/grav,joeyhenricks/a-broke-vegan,JamesPan/gravbox,sylvestrelucia/grav,userfrosting/learn,webuxr/iamrs,notklaatu/grav,dimayakovlev/grav,stell/grav,getgrav/grav,tomzx/blog.tomrochette.com,tomzx/blog.tomrochette.com,toovy/grav,notklaatu/grav,sylvestrelucia/grav,sylvestrelucia/grav,sylvestrelucia/grav,JamesPan/gravbox,Vivalldi/grav,userfrosting/learn,toovy/grav,getgrav/grav,tomzx/blog.tomrochette.com,shortsofia/testesitegrav.github.io,gigago/grav,tomzx/blog.tomrochette.com,dimayakovlev/grav