Update robopaint.es.json

Center Spiral missing from the Fill types. 

"filltype": {
        "title": "Tipo:",
        "opt0": "Línea Recta",
        "opt1": "Línea Triángulo",
        "opt2": "Línea Sine",
        "opt3": "Centro Espiral"
        "opt4": "Garabato TSP"
      },
Merge pull request #162 from RI0/patch-4

Update robopaint.es.json
Rename print mode translation placeholder file
In prep for mode translation... later.
Keep method-draw up to date with robopaint branch
Fixes #152
Merge remote-tracking branch 'upstream/master' into i18n