Show commit hash in about dialog in development

This patch adds the git commit hash to the about dialog when building in
development mode so it's easy to detect the exact version for nightly
builds.

Fix #126
1 job for commit-about in 5 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #1240107
flatpak
flatpak

00:05:49