Remove deleted files from the build system.

 - TorrentEngine (in favor of Core)
 - Update reference of Log (now exists in core, but might delete/move this one again))
Update old reference to GTorrent_Core with Core (might place in namespace)
Replace Core::getEngine()->... with simply the invoked function name, no longer need to call ::getEngine()
Move Log from shared to core (might delete/move this one again)
Delete Log duplicate
Added TorrentEngine features to Core as it's useless
Combine addTorrent and addMagnetURL functions