Target deployment date: June 12 2018
TODO
[x] The extension is added to the make-wmf-branch script, Example: https://gerrit.wikimedia.org/r/#/c/379710/
[x] A branch of the extension has been cut out and rolled out through the train.
[x] The extension has been added to the extension-list file in mediawiki-config
[x] The extension has been removed from the extension-list-labs file, Example: https://gerrit.wikimedia.org/r/#/c/390385/
[x] Add it to wgBetaFeaturesWhitelist (see James's approval below) Example: https://gerrit.wikimedia.org/r/#/c/390386
[x] Prepare configuration in IntitialiseSettings and CommonSettings so it's easy to enable the extension then applicable Example: https://gerrit.wikimedia.org/r/#/c/390386
[x] Add it to the grafana board for tracking beta feature usage Example: https://gerrit.wikimedia.org/r/#/c/392593/
[] the mediawiki.org export link message should say `Export to Test Wiki`
[] Activate FileExporter as a beta feature on mediawiki.org and test2, linking to test wiki
[] Activate FileImporter on test wiki, allowing only files from wikis from the sites table