Refactored `ResourceManager` so that most of its methods return instead of having an `out` parameter

[Lehonti]

The only exception is the LoadCssStyles method, which looks a bit more involved because it is called externally.

[cameronwhite]

The exception handling seems inconsistent here - some of the helper methods no longer catch exceptions (leaving it to the caller), while other still catch and log their exceptions

My initial thinking is that the "catch and log" approach is better in this specific case, since returning null is sufficient for the caller to decide what to do, and simplifies the code using these helper functions