Update the autoloader to support module interfaces

[jsavell]

CORAL is on its way to employing interfaces, which is good, but we should avoid requires and includes by updating the existing autoloader to find them automatically when placed in an interfaces subdirectory under a module's admin directory.

[t4k]

Can we talk about the directory name admin? While we are considering these changes, I think it might make more sense to put these things in a directory named lib or something like that. admin as a directory name isn’t optimal to me.