unify command line flags of all binaries

My apologies to anyone actually running a DCS instance for breaking
stuff, but the previous state was a mess.

We now use underscores instead of camel case for flags consistently
(e.g. mirror_path instead of mirrorPath).

Also, flags used in multiple binaries (e.g. -listen_address,
-mirror_path, -unpacked_path) do now mean the same thing, have
consistent explanation and naming.

fixes #10