Updated mediawiki/extensions
Project: mediawiki/extensions/Flow  d862ab3f861136375687726d1472fc67e7cbbb1a

Refactor header JavaScript

The chaining was a bit hard to follow & made it hard to "hook into" a specific
aspect (e.g. manually re-submit header content after an edit conflict)

Meanwhile also added fail() handler to show error if fetching content failed.
Also made outputting the errors use base's showError method.

Change-Id: I75a116f852250ab598bd86a56bfcb84d6f3e0b4f