Disable rpm, deb, tar.gz: evaluate upgrade path

[thomasnordquist]

Should just be a notification like currently in OSX.
=> Small notification top right corner
=> query github api for last release and offer a link

Debug how much the existing update already tells us about updates on linux.

[thomasnordquist]

There should probably not be a notification if it is an rpm / deb file, depending if it was installed through a distro package repository. (Why show that there is an upgrade when it is not accessible through the official distro channels. May feel infuriating if you always see that there is an update, but cannot update due to the release/update strategy of your distro)

[thomasnordquist]

AppImage is quite good, there are currently no plans for unix distro distributions