put content ratings for regions other than BR/DE under waffle (bug 943646)

**Problem:**

- some iarc waffle leak with regions+content-ratings. some games in regions other than germany/brazil are disabled due to no content rating, but for now they should be enabled.
- non brazil/germany apps are displaying content ratings on consumer pages
- germany is set to USK, but it should be set to Generic content ratings body

**Implementation:**

- put some ```mkt/constants/regions.py``` constants under a 'iarc' waffle switch
- in app resource, don't send content ratings for non-brazil/germany regions at ```dehydrate``` stage 

## Some PR Discussion

ngoke: Thanks for catching the bad logic.

```cvan: re: hide the "For ages 7+" in the header```

I can try to stop it at the API level. That way we don't have to revert/revert changes on Fireplace when as we flip the IARC switches.

```I don't understand this code. why are we checking explicitly for mkt.ratingsbodies.GENERIC?```

The Generic content rating body is special. All regions that don't fall under CLASSIND/ESRB/PEGI/USK are pigeonholed into Generic. Instead of:

    {'us': {#esrb rating}, 'pe': {#generic rating}, 'me': {#generic rating}, 'rs': {#generic rating}, etc}

We can shorten the data structure:
  
    {'us': {# esrb rating}, 'generic': {#generic rating}

And on Fireplace, if the region isn't found, it falls back to Generic.

```can you show me where we're enforcing that?```

We are enforcing it in ```mkt.regions``` in the ```ratingsbody``` attributes. But I prematurely flipped the switch on having Germany show ```USK``` ratings. Fortunately, there are no USK ratings so it'll fall back to Generic.

This patch fixes some things while the switch is off (only show Brazil + Germany ratings, force Germany to Generic).