MOB-2297 Don't update categories without changes

It's a way of things introduced by @nandy-andy, I just follow it. I guess it's more self sustaining without passing parameters around? Also I use `$this->getData( 'mapId' )` in `validatePoiCategories` where it would be straightforward to pass parameter and in `createPoiCategory`, `updatePoiCategory`, `deletePoiCategories` where it'd be passed "two levels down" (so not a perfect solution).

@nandy-andy what do you think?