OK, break some stuff. (Move FileUtills files.)

This commit moves the FileUtills.h/cpp files to a new subdirectory
called File_Management_Subsystem.

It has it's own CMakeLists.txt now, so fixing the build is fairly
simple. However it will be fixed shortly as this is really only part of
a commit. (Some restructuring.)
Add FileUtills::GetExecDirectory().

This commit adds the FileUtills::GetExecDirectory() function to
FileUtills.

(Currently Linux only, as usual.)
Add plugin support to Thread_Utils.

This commit adds runtime plugin loading support to Thread_Utils.
(In addition to mostly rewriting Thread_Utils in the process to
accomodate the changes.)
Fix Unit_Tests.

This commit fixes the Unit Test code for the previous commits.
The entire tree *should* build again with this commit.