WINDUP-152 map in props

See the jira. Core reformat if okay to merge.
It still can be blank, if stated explicitely. The question is whether we want that by default.
Reason: If blank, and ruleset author will add a map to his model, it can result in map keys overwriting other properties (e.g. type) and lead to hard-to-debug errors. Sometimes even ruleset author doesn't know in advance what data will be in the map. I'd vote for "map" as default and possibility for @InProperties(propPrefix="").

@Map - maybe. If we want to tend to hide the impl details. But that would raise the question why @Map and @AdjacentMap. Further, @InProperties Map tells clearly it's a map.