add app image download option

[jospoortvliet]

Add the appimage to download page, see
https://twitter.com/probonopd/status/840270164792872961

[probonopd]

As pointed out in nextcloud/client_theming#61:

Right now an AppImage for Linux is produced for each commit on Travis CI and can be downloaded from a temporary transfer.sh URL that is visible toward the end of each Travis CI build log. Few people will ever find it there.

Hence, please build an AppImage for the stable release (or look up the AppImage download URL of the continuous build made when the release was flagged, i.e., on this page click on the green arrow next to the RC1, scroll to the end, see the https://transfer.sh/Oz2xp/nextcloud-desktop-sync-client-git6125460-glibc2.14-x86-64.appimage link - that is the AppImage of RC1 at a transfer.sh upload location where it is temporarily stored for 14 days), upload it at a permanent location such as GitHub Releases, and link it on the download page instead of "Source":

Providing an AppImage has, among others, these advantages:

• Works for most Linux distributions (including Ubuntu, Fedora, openSUSE, CentOS, elementaryOS, Linux Mint, and others). The version that gets built on Travis CI should run on 2014-ish and later distributions
• One app = one file = super simple for users: just download one AppImage file, make it executable, and run
• No unpacking or installation necessary
• No root needed
• No system libraries changed
• Just one format for all major distributions
• Works out of the box, no installation of runtimes needed (unlike Snap and Flatpak)
• Optional desktop integration with appimaged
• Optional binary delta updates, e.g., for continuous builds (only download the binary diff) using AppImageUpdate
• Can optionally GPG2-sign your AppImages (inside the file)
• Works on Live ISOs (unlike Flatpak)
• Can use the same AppImages when dual-booting multiple distributions

[MariusBluem]

Makes a lot of sense ... lets wait until the new install page is ready (#434) - otherwise we will do this twice 😅🙈

[m4lvin]

The button is there now but with both Firefox 52.3 and Chromium 60 clicking on it loads plain text garbage into the browser instead of downloading a file. Apparently the server from which the AppImage is downloaded does not send correct HTTP headers to indicate that this is a binary file meant to be downloaded and not displayed?

[jospoortvliet]

wow, yes, can reproduce. Will fix a bug internally with sysadmin about our download server. Thanks for noticing!

[m4lvin]

Thanks for the quick reply.

Where should bugs in the AppImage itself be reported? On Debian 9 Stretch I ran into "error creating ssl context (error:140A90C4:SSL routines:func(169):reason(196))" as described here https://help.nextcloud.com/t/nextcloud-client-appimage-version-2-3-2-ssl-problem/19870

[jospoortvliet]

@m4lvin pls use the client_theming repo for now... https://github.com/nextcloud/client_theming

Thanks!

Meanwhile, this was fixed, so let's close.