Add the ability for the Ark server to run in any namespace.
Add `ark client config get/set` for manipulating the new client
configuration file in $HOME/.config/ark/config.json. This holds client
defaults, such as the Ark server's namespace (to avoid having to specify
the --namespace flag all the time).
Add a --namespace flag to all client commands.
Signed-off-by: Andy Goldstein <andy.goldstein@gmail.com>
