#2837 Startup Slowdown when config in ini vs. config in reg

To continue the discussion on [#2837](https://trac.mpc-hc.org/ticket/2837).

`GetPrivateProfileSection()` turned out to have severe limitations, thus a full parser.

Didn't find a way to bulk read the registry, no changes there.

This should bring .ini startup times on par with the registry ones.

Should break no external things, but further testing/insight is needed.