Notify when the version is out of date

It is fairly common for folks to be running older versions of the plugin without realizing it, and JetBrains does not appear to make any effort to notify about out of date plugins or to keep them up to date.

So, we should implement our own check and show a notification if out of date.

**Edit**: also the situation is weird with Gateway having its own set of plugins, and then also the IDE itself has a client set and host set, so checking the version manually is not straightforward and showing a notification with a link to the right spot would be helpful.