Use sftp for deploying remote components instead of scp. sftp has the
advantage that it can also create directries, chmod files etc., so
that we can do everything in one call of sftp instead of mixing scp
and ssh calls.
The downside of sftp is that it can't switch to ~ resp. %userprofile%
for the remote side, and we have to assume that sftp starts in the
user's home dir. This is the default and works on my machines!
cdc_rsync and cdc_stream check the CDC_SFTP_COMMAND env var now and
accept --sftp-command flags. If they are not set, the corresponding
scp flag and env var is still used, with scp replaced by sftp. This is
most likely correct as sftp and scp usually reside in the same
directory and share largely identical parameters.
Adds a ServerArch class whose job it is to encapsulate differences
between Windows and Linux cdc_rsync_servers. It detects the type
based on a heuristic in the destination path. This is not fool proof
and will probably require further work, like falling back to the other
type if the detected one doesn't work.
Uses the ServerArch class to determine the different commands to start
the server and to deploy the server.
Note that the functionality is not well tested on Windows yet, but
copying plain files works.
