No longer store variation sequences explicitly. Instead, put a 0
in the sequence where the modifiers will be inserted. This is more
compact, and it allows us to put variations directly into the
recent section.
Update the type of the recent-emoji setting to match these changes.
The json file is imported from the (MIT-licensed) emoji.json[0] node
module, which generates it from the emoji list published by the
Unicode Consortium.
This commit also adds a little tool to convert the data into
a compact GVariant, and the result of that conversion, which is
added to libgtk as a resource. The following commits will make use
of it.
[0] https://github.com/amio/emoji.json
