libcore|Xcode: Fixed a bunch of benign integer conversion warnings
OS X|Xcode|qmake: Script for generating an Xcode workspace

The Qt 5.3 qmake is incredibly broken when it comes to generating
Xcode projects, but this commit adds a script that cobbles together a
fully functional workspace that contains all the individual
projects that qmake generates.

xcode_workspace.py generates a workspace called "Doomsday.xcworkspace"
to the current folder.
Fixed|InFine: Compiler warnings (un/signed comparison; string literals)