add file picking for osx and ios and implement equirectangular import

engine/image.cpp

@@ -23,6 +23,15 @@ bool Image::load(std::string filename)
     return true;
 }
 
+bool Image::load_file(std::string filename)
+{
+    stbi_set_flip_vertically_on_load(false);
+    uint8_t* buffer = stbi_load(filename.c_str(), &width, &height, nullptr, 4);
+    comp = 4;
+    m_data = std::unique_ptr<uint8_t[]>(buffer);
+    return true;
+}
+
 void Image::flip()
 {
     auto flipped = std::make_unique<uint8_t[]>(width*height*4);