Fixed an embarrassing merge error from waaay back. Didn't disrupt operation but caused funny error messages in the log.

Thanks to @nophead for reporting this.

Closes #433
Create CONTRIBUTING.md
Bug fix for Emergency Stop
Merge pull request #475 from Salandora/master

Bug fix for Emergency Stop
Insert src folder at first position of sys.path
Merge branch 'master' into devel

Conflicts:
	src/octoprint/server/ajax/control.py
Versioning by versioneer: https://github.com/warner/python-versioneer/