Minor improvements in the loading of the preferences on macOS

As discussed in the aftermath of !85 (merged). This cuts out the defaults export command from the prefs loading pipeline which isn't really needed. While I was at it, I also fixed up some wrong help paths in the default prefs (apparently inherited from Pd-extended), so that these point to Library/Pd-l2ork now.

Tested on Sierra, works fine for me. Default prefs are still loaded if no user prefs are present, and UTF-8 in the prefs also still works.