General RPC configuration improvements

Separate the `rpc_addr` parameter into independently configurable `rpc_address`
and `rpc_port`, allowing a blank `rpc_address` to disable RPC service. Add an
`rpc_auth` parameter which sets the auth token for RPC requests.
`install_path` no longer has a trailing slash
Merge branch 'simplify-installers' into multiple-fixes
Merge branch 'movealong' into rpc-improvements