Function load_source_data problem

[pixelRBT]

The function load_source_data will reorder the sources by their name in the order of alphabet or number (for example, the original order of the sources was a c b, the function will reorder it into a b c) instead of using the original order. This can cause further issues like a mismatch of the sources and their prior information. It would be nice to solve this problem or give users a choice to disable the ordering process.