type/tech in hostmanager

[a-gerhard]

like in templates, there is confusion between type and tech in the hostmanagers, since the hostmanger's type attribute is equivalent to backend/webfrontend tech attribute.
We should completely get rid of a 'type' in the hostmanager and only use "tech".

This should be done when the hostmanager is stable, i.e., when @swuest has merged his current changes request.