v0.7.4 released

Just a couple of tiny quality-of-life fixes on this:

• There’s now an “open manual” command in the help menu
• If butler isn’t configured, the itch.io upload checkbox is disabled (reduces confusion)
• New itch.io uploads will now use the html target (instead of preview), so itch can auto-detect that it’s a web preview

With that last one, existing albums will continue to use the preview channel if it already exists, but it’s recommended that you rename your preview channel to html (or delete it outright and reupload).