Switch Spyder Environment without installing spyder at each environment

(Spyder maintainer here) We added some improvements in our 3.3 versions to help users deal more easily with multiple environments. Please see this blog post for the details, in particular the section called Even more fixes and refinements with Spyder 3.3.1.

Note: A little bug that affects this surfaced after we released 3.3.1, just in case you find that problem too. A fix will be available in 3.3.2, and more improvements on how to handle conda environments are planned for Spyder 4, to be released in 2019.