Slack 4.23.0

Depending on how the app was installed, the "Launch on Login" option was sometimes appearing greyed-out, visible but inaccessible, like a storefront window display after closing hours. We've unlocked the door, flipped on the overheads and fired up the neon "Open" sign. Come on in and have your pick of all the preferences. Some external URLs were occasionally launching within the Slack app window, but will now load in your default web browser, as is proper. Slack cannot have a little web page, even as a treat. This release includes security improvements. Updating is recommended.