Add mcplot toggle to "plot 1D-curves from 0-value" in linear mode

[willend]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

• Add mcplot toggle key to "plot y-value to 0" in linear 1D-curves. Handy with possibility to scan --seeds in mcrun
• Enable SVG hardcopies on Windows - tested functional.

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

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