AGPUSH-980 : Export installation + UI

This PR contains a first version of the export service + UI 
Please note that the import UI is not yet there and will be provided in a separate PR 
screencast : https://www.youtube.com/watch?v=HFXesTHh4PM&feature=youtu.be

For Master only

@edewit @matzew @abstractj  Could you review please ? 
Ah, the `/registry/device`.

How about moving to a class that is dedicated to exporting the bits?

/ag-push/rest/export/{variantID} ?