Generate and upload AppImage, closes #11

[probonopd]

This PR, when merged, will compile this application on Travis CI upon each git push, and upload an AppImage to your GitHub Releases page.

Providing an AppImage would have, among others, these advantages:

• Applications packaged as an AppImage can run on many distributions (including Ubuntu, Fedora, openSUSE, CentOS, elementaryOS, Linux Mint, and others)
• 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
• Works out of the box, no installation of runtimes needed
• 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
• Can use the same AppImages when dual-booting multiple distributions
• Can be listed in the AppImageHub central directory of available AppImages
• Can double as a self-extracting compressed archive with the --appimage-extract parameter
• No repositories needed. Suitable/optimized for air-gapped (offline) machines

Here is an overview of projects that are already distributing upstream-provided, official AppImages.

PLEASE NOTE: For this to work, you need to enable Travis CI for your repository as described here prior to merging this, if you haven't already done so. Also, You need to set up GITHUB_TOKEN in Travis CI for this to work; please see https://github.com/probonopd/uploadtool. If you would like to see only one entry for the Pull Request in your project's history, then please enable this GitHub functionality on your repo. It allows you to squash (combine) the commits when merging.

If you have questions, AppImage developers are on #AppImage on irc.freenode.net.

[probonopd]

A test AppImage is available at https://github.com/probonopd/ZeGrapher/releases

I think it has some issues finding some of its icons, could it be that they are referenced in terms of absolute paths rather than relative to the main application? In this case, you could use QString QCoreApplication::applicationDirPath() and construct a relative path to the resources from there.

[AdelKS]

Hello! First, thank you for your contribution @probonopd . For the icons not appearing, I have been designing these past days SVG ones since Qt seems to support them in one of its latest version, is it possible to put Qt version to for example 5.11.1, for which the icons seem to get rendered ?

[probonopd]

Unfortunately, 5.11.1 is not available for Ubuntu 14.04, which currently is the oldest still-supported Ubuntu LTS release.

[AdelKS]

Okay then, let's keep it as it is for now and we'll update it when a newer Qt version is available. I'll switch back to PNG versions for now. Thanks!

[probonopd]

Thanks for merging. However, the AppImage is still missing. The build log says:

$GITHUB_TOKEN missing, please set it in the Travis CI settings of this project
You can get one from https://github.com/settings/tokens

You need to set up GITHUB_TOKEN in Travis CI for this to work; please see https://github.com/probonopd/uploadtool.

[AdelKS]

Right... I forgot that part of the process :laughing: Let me look it up!

Edit: Done, I was wondering why I didn't get an AppImage in the releases.

[AdelKS]

@probonopd your fix works! The current latest AppImage has all the icons, I didn't change them to PNG.

[probonopd]

https://appimage.github.io/ZeGrapher/ :+1: