Add tag for 1.4 release

[fingolfin]

Version 1.4 was released 03/08/2017 according to its PackageInfo.g file, but there is no git tag for that version, unlike for all previous reasons. It would be really nice to have such a tag, so that one can quickly see what exactly changed between released.

I tried but could not identify which commit this released was made from: there is a commit on 2017-02-17, which is immediately followed by one from 2018-09-18 ?

[bh11]

I've (re-)pushed the tag to the Git repository – no idea why it wasn't pushed before.