Show notification on long env load

[cab404]

Some environments, especially Nix ones take a lot of time to load when are not cached. That means blocking everything until they load, without any info to user.

A status bar would be helpful. Since first load should always be synchronous, add a timeout to it. If it times out (configurable timeout), show "Takes too long to load" message, and start loading it in background, updating status bar/notification/debugging window with latest console messages.