Cura integration

This will enable the client to upload an STL to Octoprint or to the SD card of the printer. It will take the STL and slice it using Cura and a provided configuration file. There is an addition the the settings panel that allows you to point to where Cura is installed for your machine and to where your configuration is that you would like to use. This relies on a patch to Cura to enable passing in a configuration when calling Cura from the command line.