classification(s) support in XML file, possibly better facilitate kid UI mode.

[LiquidDivide]

With the ui-modes pull request, I have been thinking it would be cool to be able to support parental guidance rating information (SkraperUI already scrapes it and calls it 'classification') such as ESRB or PEGI or such in the gamelist.xml file. Having this information displayed in ES as a first pass would be great, but my ultimate desire would be to then configure a threshold based on those ratings to auto-hide games in kid ui mode. I know this information is only available for newer games (~1994 and later), but it would be pretty cool to do this instead of having to manually apply a <kidgame> tag to everything I'd rather my children not play. At least, it would give some of us parents a better starting point to then add <kidgame> tags where we feel differently.

I see this as working with a <classifications> tag that can support multiple <classification> tags. something like

<classifications>
    <classification>
        <org>ESRB</org>
        <rating>T</org>
    </classification>
    <classification>
        <org>PEGI</org>
        <rating>12</org>
    </classification>
</classifications>

I'm only aware of ESRB and PEGI for parental guidance with games, but I'm sure there are others. I know screenscraper.fr and thegamesdb already provide this information to scrapers.

One could then configure the order and threshhold for each classification system to hide games. So, I could essentially say hide everything that is ESRB: Teen and higher (which would include Teen, Mature, and Adult Only). If a game doesn't have ESRB, then we could fall back to say hide anything that is PEGI 12 and higher, etc. If a game has no classification, do not hide it (so that NES and old arcade games and such remain available), or have another config setting that lets me decide whether to hide or show games with no classification.