implement messaging for __group type

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
implement messaging for __user type

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
make default values for optional_multiple parameters work

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
Merge remote-tracking branch 'steven/issue/239'
++changes(3.0.0)

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
Merge remote-tracking branch 'steven/issue/236'

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>

Conflicts:
	cdist/conf/type/__user/gencode-remote
++changes(3.0.0)

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>