Compass, many bug fixes, linux problems solved
Added checkpoints, which allows the user to restore a previous state on the fly in case printing fails. Still needs more work. Removed dependency of .NET 4 (Returned to .NET 3.5).
Merged last changes from repetier
Fixed concurrency problem when started printing (only happened in linux with mono)
Improved Checkpoint dialog. Replaced the list of checkpoints with a control with next, previous, etc, that displays the current checkpoint position and allows moving the extruder while viewing it.
Use absolute path for Arrow loading, change arrow color depending on homing state, prevent sleep mode during print on windows.
Added @continuedScript when restoring state, added checkpoints configuration, fixed a bug when disabling checkpoints every N movements, and removed some development comments
Added an index to checkpoint positions in memory, which dramatically improved the search time for feature 'go to current position' when printing big models (tested one with more than 650k lines).
Merge remote-tracking branch 'origin' into checkpoints

Conflicts:
	src/RepetierHost/Main.cs
	src/RepetierHost/Main.resx
Created an abstract class for the PrintingState, which is later used by checkpoints and snapshots. In order to do that, modified the way xml are generated, to make it less code dependant.
Now checkpoint names are generated when needed based on the checkpoint type instead of keeping it stored in memory. Replaced the usage of a checkpoints LinkedList with a BasicList that uses a LinkedList internally. This will allow us to replace it with a file based list for large files. Enhanced checkpoints window. Changed the code that generates the GCode to restore state, so that it uses StringBuilder more than it was using before.
Fixed a bug when restoring state: E was set before pausing, which causes a retraction after pausing. Added Go to next/previous layer in Checkpoints dialog. Fixed some translations.
Enhanced the checkpoints dialog (added go to next/previous layer, lock z). Fixed a couple of small issues.
Fixed a bug when searching checkpoints for nearest coordinates.
Added Apache License header to some files I had written that didn't have.