Is there a resource/website that has list of all possible datasets from around the world with links to the download page, names of columns in the individual datasets (so users can search by a particular column name if they wish to), descriptions, usage terms etc?
No. Though there's various parties trying to build or assemble such a collection, I've found the external links from this wikipedia page to be quite a good start:
(it lists websites such as https://datahub.io/)
Furthermore, the EU has recently started a project to make all scientific data 'FAIR' (or 'Findable, Accessible, Interoperable, and Reusable') within this decade, you can read about that here: http://ec.europa.eu/research/openscience/index.cfm