[WIP] Add support for snapcraft

[mkljczk]

I've put together this pull request to add a snap package. I've tested it on Ubuntu 16.04 and 17.10, but it should work just as well on Ubuntu 14.04, Linux Mint, Manjaro, Debian, OpenSUSE, Solus, etc.

If you merge and npm run build-snap on an Ubuntu 16.04 VM with an appropriate version of node installed it will create dist/sqlectron_VERSION_amd64.snap.

Copy this to a Linux system, enable snap support, then run:
sudo snap install --dangerous sqlectron_VERSION_amd64.snap. Execute it with sqlectron from the terminal or find it in the desktop launcher.

If you create a developer account and push this to the Snap Store, it can be discovered and installed through GNOME Software and https://snapcraft.io/discover. To create the developer account, sign up here, then register the "sqlectron" name.

You'll need the snapcraft command to push the snap file to the store.

• If you're on a Mac, you can brew install snapcraft
• If you're on Linux, it's sudo snap install --classic snapcraft

Then you can push it to the store out with:
snapcraft push sqlectron_VERSION_amd64.snap --release stable

[maxclaus]

@m4sk1n Thanks for this PR. I'm downloading a VM with Linux to test it out. Could you please check why the build is failing on Travis?

[come-maiz]

Hey @m4sk1n, this travis job runs in trusty, and snapcraft was added to the archive in xenial. You can try this:
https://docs.travis-ci.com/user/installing-dependencies/#Installing-Snap-Packages
Or use a xenial lxd or docker container.

[mkljczk]

@maxcnunes I don’t know why it doesn’t pass AppVeyor build, I haven’t even touched anything related to Windows…
Now it skips building snap, should I make it test snap building in container?

[maxclaus]

@m4sk1n Although you have not changed any specific Windows building code. You have upgraded the electron-builder which by the semver pattern it has some breaking changes. But, by looking elecron-builder docs I can't find if it really has anything that should impact our current configuration.
I saw electron-builder is working to fix that: electron-userland/electron-builder#2458
You could downgrade that to 19.52.1 which seems to not have that issue.