As some plugins are becoming big now, it is hard for the user to know, if the plugin
is being downloaded or just nothing happens.
This commit adds a progress bar during download, which can be disabled by using the `-q`
parameter.
In addition this updates to jimfs 1.1, which allows us to test the batch mode, as adding
security policies are now supported due to having jimfs:// protocol support in URL stream
handlers.
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