inventory: add Windows, Mac OS X, and LSB modules

Add a LSB module that's only used on non-Windows, non-Mac OS X hosts.  Call `/usr/bin/lsb-release -a` and parse the results.  Once https://github.com/cfengine/core/pull/1021 is available I 
can use it here to construct nice class names (and will have to exclude 3.5 hosts then).

Add empty Windows and Mac OS X modules.