export: generate & download csv

move table generation code into Export class to use it from client & from server
add Exports FS.Collection
add method createCSV(selection, loginToken) which generates a csv, saves it to the FS.Collection and returns the download url to the client
add package synced-cron
add cron which deletes Exports cfs collection entries which are older than 20 mins
spinner for download button
styling