Add snap package for Linux

[pat-s]

Working snap package for Linux.
Testing via snap install pats-franz --edge

Open test call at the snap forum: https://forum.snapcraft.io/t/call-for-testing-franz/4132

To work with travis and automatic deployment, see https://docs.snapcraft.io/build-snaps/ci-integration.
Essentially, you need to run snap enable-ci travis with travis-cli installed after merging the PR. Then Travis will be encrypted with the correct credentials.

It is recommended to also upload a version to channel "stable" for every release.
Currently, only apps in channel "stable" are discoverable via snap find.

[guilhem]

any news?

just for the record, command is snapcraft enable-ci :)

[pat-s]

Seems there is no interest in a snap package here. Feel free to re-open.

[matbrgz]

That's amazing work.. keep it.

[sverhagen]

Snap packages are great. Non-Linux users publishing packages as .deb seem unaware that these don't auto-update. This work is valuable, though, I'm sure, your audience is a niche.

I was wondering, looking at the proposed changes, whether you wouldn't want to leverage the support for Snap images that comes with electron-builder? How I understand the proposed changes, it seems you're rolling your own?