Bowden e3d v6 mount for piezo holder

Added a collar to the top piece of the piezo holder, so that you can install the bowden tube pneumatic connector there.

##### Printed the original, but am guessing that its meant for use with an original e3d v6 and/or Titan - it doesn't fit very well with my clone e3d v6 or my clone Titan extruder. As a workaround I have shimmed the neck with a small piece of sillicone.

My changes to Marlin configuration.h to get this to work :

- Uncomment //#define SN04

- Uncomment //#define BILIN