Add version numbers from git tag and commit

[remyroy]

I added the version number and commit hash from git in the window title but it could also be added in the UI at the bottom for #87 .

When doing a release, all we need to do is add a proper tag in git (starting with v, like v0.8.1), update the version number in package.json and build from there to have version show automatically with hash. This matches github release suggested tagging practices.

Related to #51 .

Closes #67

[remyroy]

This is how it looks when bundled

.

We also have access to BRANCH if we want to show the current branch name and LASTCOMMITDATETIME to show the last time there was a commit.

[remyroy]

This makes the git latest tag the ultimate source of version number. We should still update version number in package.json but that one is only going to be used with electron-builder (for the final distribution file name for instance). I'm not sure if we can plug those together.