Re-implemented plugin loading.

Using a multi-threaded loader member function from the game class.

This currently produces invalid cyclic errors for me though, so I need
to fix that.
Fixed broken plugin loading.

Some plugins were being repeated or overwritten.

Masterlist messages are currently not being displayed for plugins in the
report though, I think I know why.
Fixed masterlist and userlist messages not shown.

It's a bit messy, ideally I'd like to have the graph store pointers or
references to the temporary plugin lists's contents.