Replace usage of SpecialPage::getTitle with getPageTitle

Was deprecated in 1.23, see Icdcf5d5295ef5e7f08b1d403e0c123f78738fd40

Change-Id: If3bcfe0dd97f77cbf8c75f8983167fd8075c2cbd
Pass context to HTMLForm, don't use HTMLForm::setTitle

Change-Id: I5d6539bb316c82e4e1f0b09ce03265d02000bc76
Migrate to JSON i18n

Procedure per https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php
with shim.

Change-Id: Ic2988d5b39691843258c0d744fda17d1f6c418c3