[cdc_stream] Add a CLI client to start/stop asset streaming sessions (#4)

Implements the cdc_stream client and adjusts asset streaming in
various places to work better outside of a GGP environment.

This CL tries to get quoting for SSH commands right. It also brings
back the ability to start a streaming session from
asset_stream_manager.

Also cleans up Bazel targets setup. Since the sln file is now in root,
it is no longer necessary to prepend ../ to relative filenames to
make clicking on errors work.

cdc_rsync/params.cc

@@ -73,10 +73,10 @@ Options:
 -R, --relative            Use relative path names
     --existing            Skip creating new files on instance
     --copy-dest dir       Use files from dir as sync base if files are missing
-    --ssh-command         Path and arguments of SSH command to use, e.g.
+    --ssh-command         Path and arguments of ssh command to use, e.g.
                           C:\path\to\ssh.exe -F config -i id_rsa -oStrictHostKeyChecking=yes -oUserKnownHostsFile="""known_hosts"""
                           Can also be specified by the CDC_SSH_COMMAND environment variable.
-    --scp-command         Path and arguments of SSH command to use, e.g.
+    --scp-command         Path and arguments of scp command to use, e.g.
                           C:\path\to\scp.exe -F config -i id_rsa -oStrictHostKeyChecking=yes -oUserKnownHostsFile="""known_hosts"""
                           Can also be specified by the CDC_SCP_COMMAND environment variable.
 -h  --help                Help for cdc_rsync