Secrets-support for binary files

From time to time I need to deploy a p12 certificate file (or similar) I don't want to keep in plain text in the deployment. 

To deploy the actual file I can use batou.lib.file.BinaryFile, but I think we are lagging a good way to put the content to the secrets. 

`./batou secrets edit <env> <filename>` is depending on $EDITOR and it become complicated to add a binary file with vim. 