Currently we show any errors that occur when saving a connection on the main view of the connections page. We should instead show a toast when errors like this occur. These errors can occur while a user has just successfully connected, so they should be at a higher level than the connections as that component unmounts after connecting.

It could use a bit more investigation, but this could probably be done with a react context in compass-components that parts of Compass can use for showing toasts. compass-home would then be the part that gives the provider for this context and renders the toast that uses it.
Currently the only leafygreen toast we show is when a user copies a connection string. Let's also move this toast to this new toast provider.