Multi-Stl-load, codeblocks support, autocenter, bug fixes

While integrating curaEngine into Repetier-Host I had to make some modifications, which should be part of the default curaEngine as well:
1. Added autocenter option to prevent centering (standard stays centering). That way the stls I send from the host stay where the user put them.
2. Upload more then 1 stl over commandline. Same trick as you do with socket sending, just over commandline.
3. Added setup to compile with codeblocks on windows. This is handy to set up since codeblocks comes with gnu compiler bundled. Visual C++ seems not to compile the code.
4. Implementation of raft air gap was wrong. Fixed it. Test with 10mm gap to see the difference.