Changes

Prevent Reflection errors from other mods tanking MJ

Avoids using the KSP.IO.File.Exist<T>() API that walks the loaded
assemblies and throws, looking for the path to the assembly with
the type T.

The MuUtils helper replicates the side effect of this API of
creating the directory.

Since we construct the path afterwards anyway to load the file the
only reason I can see for the reflection-driven-API is for that
side-effect, and to cause weird bugs if someone ever moves the DLL
location around and makes the two APIs start to disagree.
 (commit: a80de9e)