Input text widgets still using std::unique_ptr<char[100]>

[andreamancuso]

Right now, input text fields are still backed by std::unique_ptr<char[100]>. This was meant to be a temporary thing.

Dear ImGui offers a safe InputText(const char* label, std::string* str) overload in imgui_stdlib.h, but it requires a proper std::string, not a raw pointer.

I should replace all std::unique_ptr<char[]> with std::string where used for user input