[evita] dom: Use |Event.Names.ATTACH| and |Event.Names.DETACH| constans names instead of string literal.
[evita] views: Use |views::TabContent| and |domapi::TabData| for |Tab| in |views::TabStrip| instead of TCITEM.
[base] Move |#pragma warning(disable: 4625 4626)| to "base/observer_list.h" from each use site.
[evita] dom/public: Introduce "domapi::TabData::operator==(TabData&)|.
[evita] views: Introduce |views::TabDataSet::Observer| for updating tab on multiple files dropping.
[evita] views: Utilize |views::TabDataSet::Observer| to update tab when tab content state is changed, e.g. multiple files dropping.