* [imgui-sfml] Add new package ImGui-SFML
* Static build only to match with `imgui`.
* [imgui-sfml] Fix case-sensitive imgui package name
* [imgui-sfml] Require C++11
* [imgui-sfml] Include IMGUI_API define
* [imgui-sfml] Remove delegating ctor - C++11 is not required
