Move applications_postfix to Ansible adapter

In its current incarnation, the applications_postfix configuration
parameter, along with the concept of "groups" is only relevant to
Ansible. Therefore, in the interest of simplicity, move it out of the
main code and into the Ansible adapter.

Signed-off-by: martin f. krafft <madduck@madduck.net>
Initial version of a Salt adapter

Signed-off-by: martin f. krafft <madduck@madduck.net>
Move Salt-internals to Salt's reclass adapters

The Salt reclass_adapter plugins now hide all the internals and provide
reclass only with the information it needs, without having to make
assumptions about Salt internals.

Signed-off-by: martin f. krafft <madduck@madduck.net>
Add README for Salt integration/adapter