It should be input first, output second, like with all other APIs. I
remember I was trying something else here, but that didn't really make
sense in the end. Also took that opportunity to get rid of one
std::string.
The original signature is a deprecated alias to the new one and will be
removed in a future release.
There will be Flag::FlipY for images at some point, enabled by default
for compatibility with existing GL code, and so it makes sense to start
discouraging setFlags() as early as possible to avoid people resetting
the default by accident.
Also update the imageconverter, sceneconverter and shaderconverter utils
to use these instead of setFlags().