Make `target_area` and `color` a member of GeoDiv instead of InsetState

[adisidev]

It makes sense to store information about the GeoDiv's target area and color in the GeoDiv itself rather than as a map in inset state.

[nihalzp]

Apart from target_area and color, the following data member info should also be a part of GeoDiv, instead of InsetState:

• std::unordered_map<std::string, double> area_errors_;
• std::unordered_map<std::string, bool> is_input_target_area_missing_;
• std::unordered_map<std::string, std::string> labels_;