Wing delta

Upon trying to compile the Marlin_v1 using the example_configurations/delta/* I encountered an error with the definition of the float delta and DISABLE_INACTIVE_EXTRUDER. 

* Added an #ifndef DELTA  wrapper around the 'static float'. 
* Added a #define DISABLE_INACTIVE_EXTRUDER true  to the example_configurations/delta/Configuration.h since it is present in the other configuration files, including the default one in the Marlin folder.