Visually deprecate old multipolygon styles

[stoecker]

Currently we still support old styles of multipolygon see ElementStyles.java​. I think it is time to somehow deprecate them more than we do now.

• So probably first is to disable the VERY old method of inner=outer completely.
• second is to never display outer styles for complete multipolygon anymore.
• Third is probably to visually mark the no-style on multipolygons as bad for these cases, where the outers have one common style.

Probably instead of removing code, we can turn it of with a default-false variable?