Gallery: use thumbnails of images for the album thumbnail
Gallery: use thumbnails of images for the album thumbnail

The thumbnails were already generated in this function, but now we save them
for displaying of the album.

Ardinis/server,IljaN/core,pixelipo/server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,IljaN/core,cernbox/core,pmattern/server,xx621998xx/server,jbicha/server,owncloud/core,lrytz/core,bluelml/core,jbicha/server,jbicha/server,andreas-p/nextcloud-server,sharidas/core,sharidas/core,IljaN/core,nextcloud/server,xx621998xx/server,sharidas/core,IljaN/core,nextcloud/server,pollopolea/core,pmattern/server,pollopolea/core,Ardinis/server,IljaN/core,xx621998xx/server,owncloud/core,pmattern/server,endsguy/server,cernbox/core,pixelipo/server,owncloud/core,pollopolea/core,cernbox/core,pollopolea/core,lrytz/core,bluelml/core,andreas-p/nextcloud-server,xx621998xx/server,whitekiba/server,andreas-p/nextcloud-server,cernbox/core,Ardinis/server,Ardinis/server,andreas-p/nextcloud-server,endsguy/server,owncloud/core,endsguy/server,lrytz/core,sharidas/core,whitekiba/server,owncloud/core,endsguy/server,pixelipo/server,jbicha/server,endsguy/server,whitekiba/server,Ardinis/server,bluelml/core,phil-davis/core,bluelml/core,sharidas/core,nextcloud/server,michaelletzgus/nextcloud-server,pmattern/server,lrytz/core,xx621998xx/server,jbicha/server,pmattern/server,nextcloud/server,pixelipo/server,whitekiba/server,lrytz/core,michaelletzgus/nextcloud-server,pollopolea/core,cernbox/core,pixelipo/server,whitekiba/server,bluelml/core,andreas-p/nextcloud-server