[Statie] add generator elements (post) ids as keys while sorting them

[TomasVotruba]

So this doesn't have to be done manually all over the place: https://github.com/pehapkari/pehapkari.cz/commit/98d115832b147cc4214481061c170bcb06366cc4

[TomasVotruba]

• make sure ids are not duplicated