Package as a snap about ubports-installer

[NeoTheThird]

Indeed, some work is already done, but looks like it hasn't been touched in a while. This issue is more about the infrastructure, and a reminder to fiddle with it.

[timsueberkrueb]

Hey, looks like there is already snap packaging in the snapcraft folder, or am I missing something?

Two questions:

• Is there a specific reason for using snapcraft/snapcraft.yaml instead of snap/snapcraft.yaml and source: <git url> instead of source: .?
• What about building it automatically with build.snapcraft.io or are you even already using your own infrastructure?

It also looks like electron builder supports snaps now: https://www.electron.build/configuration/snap.