Remove un-used locals from moment

[falconmick]

moment is currently 1/3 of our package size with 4/5 of that being locale files... According to this post you can remove all locals except the ones you want via:

new webpack.ContextReplacementPlugin(/moment[\/\\]locale$/, /en/)

Might be worth waiting for #80 to have it's PR complete as analysing that it's removed the locals we don't use could be useful.