add mapcss from PowerQA ValidateMyGrid

[nlehuby]

This PR add a mapcss ruleset about power grid & power generation, that is already packaged and available for JOSM.

source code: https://github.com/open-energy-transition/validate-my-grid
doc: https://wiki.openstreetmap.org/wiki/Power_networks/Quality_Assurance

The translations for the rules and the Osmose doc is intended to be in the validate-my-grid repo too, following the same models as Jungle Bus transport_mapcss ruleset (but I will come eventually, there are no translations in the repo for now)

#MapYourGrid

[nlehuby]

the item number was chosen randomly

[nlehuby]

I had troubles with the rules that use the link selector, that is apparently not supported in Osmose mapcss:

even with the -osmoseItemClassLevel: none; flag, I got the following error at compilation:

line 315:30 no viable alternative at input '[role!~'
line 315:30 mismatched input '!~' expecting {',', '{'}

mapcss:

relation[power=circuit] >[role!~/^(section|substation)$/] way {  
   throwError: tr("Wrong role for way in power=circuit relations");
   suggestAlternative: "section/substation";
   -osmoseItemClassLevel: none; /* The rule involves multiple objects, which is not yet supported by Osmose */
}

source: https://github.com/open-energy-transition/validate-my-grid/blob/gh-pages/powerQA.validator.mapcss#L315