This is the first of a number of PRs aimed at helping admins manage their translation overrides. It simply adds a list of available interpolation keys below the input field when editing an override.
It also includes custom interpolation key.
"I18n.t(key, locale: locale)" fails to find the correct translation in some cases. We should always wrap it with the "I18n.with_locale(locale)" method.
Also, reverting an override wasn't always possible because the serializer always used "I18n.locale" as the locale.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
Ted Johansson
Roman Rizzi
Osama Sayegh
Gerhard Schlager
Sam Saffron
Guo Xiang Tan
Robin Ward