Refactored masterlist updating code.

Also refactored plugin loading code, but that's still WIP.
Sorting and editor init now use game lists.

Rather than temporary metadata list containers.
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.
Renamed network.cpp to git.cpp

Gives a better indication of its content.
Fixed API compilation.
Removed use of unnecessary current game reference.
Started to refactor plugin sorting code.
Refactored more sorting code.
Refactored game selection code.
Refactored userlist comparison code.

Also improved editor userlist output, and some const correctness
improvements.