Merge pull request #374 from GreatFruitOmsk/master

Fix crashes on Mac OS X 10.6 and CPUs without SSE4
Do not show loading... when the file fails to load.
Update on the file load error.
Update on the file load error.
Merge branch 'master' of github.com:daid/Cura
Speed up GCode loading a bit.
Slight speedup on gcode loader.
Better display dual-extrusion paths.
Update for dual-extrusion. Better start code with multiple temperatures set.
When stiching dual-extrusion remove all the moves between layers and give the switching code a new position to move to.
Add temperature settings for nozzles 2 to 4.
Add different filament diameters for multiple extruders.
Update cura.desktop

Added path to cura.desktop in order to fix slicing errors on Ubuntu.
Update requirements.txt

Added missing prerequisites/dependencies for Ubuntu. 
Update README.md

Added build instructions for Ubuntu.
Merge pull request #377 from dylanwinn/master

Fixed errors in Debian packaging.
Remove the cx-freeze requirement.
Remove the default Estep value bug. Add enter to the number entery gl control.
Goto the next wizard page if the skip button is pressed.
Reset the window position if the window is off-screen.