EquipmentProperties: added ramp related properties

[k00ni]

reference: https://github.com/sozialhelden/ac-format/issues/10

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last question from the related issue

Regarding "rampSlope"

I would use ~~rampGradient~~ rampSlope, because it seems the best translation for "Steigung der Rampe" (source).

What measure/attribute is to use here? My data is currently modeled using percent, like 6%. @opyh I know we may discussed this yesterday, but i couldn't remember, if we came to a decision here.

What do you think?