Nice detailed step-by-step instructions on moving calendar and contacts into ownCloud from Google services.
"Over the last few years, Uber and Airbnb have come to be known as leaders of something called the sharing economy.
Give their founders credit for this feat of mostly misplaced nomenclature. The companies help people sell rides in cars and rent stays in homes; they deserve no more credit for promoting a skill learned in preschool than Marriott or taxi companies."
It explains how to add Add-ons from files (mouse-over on the Download button). Icedove/iceowl Add-on search has an option for installing from a file.