Update Makefile to newer arduino and fix upload issues

This patch updates the Makefile allowing 'make upload' to work more
reliably by using 'wiring' rather then 'arduino' as a programmer.

Additionally it sets more common arduino files/location for non windows
users.

Windows users tend to use _do_make.bat which overrides these values
anyway.

Fixes Ultimaker/Ultimaker2Marlin#44

Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>
Add electroncis_test to Makefile so that the linker is happy again

c1e1060 added the electronics_test function, but did not add it to the
Makefile. This patch fixes up the Makefile so that the linker can link
the firmware again.

Fixes Ultimaker/Ultimaker2Marlin#45

Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>
Merge pull request #47 from oliv3r/issues/45

Issues/45