Setting available languages

[michaelbromley]

There is currently no way to set which languages should be available to translate translatable entities into.

Where should the available languages be set?

• Per Channel. This would not work if there are translatable entities which are not channel aware.
• Globally. Then we would need some global settings location. We already have the VendureConfig object, but perhaps there should be a database-level config registry for dynamic settings which can be changed via the admin ui.