Make BEM.JSON compatible with BN and bh

Now this works well
```
//outer bem.json
BEM.JSON.decl('mix-use-outer-bem-json-block', {
    onBlock: function (ctx) {
        ctx.content({
            block: 'mix-use-bem-bn-block'
        });
    }
});
//inner bem.json
BEM.JSON.decl('mix-use-inner-bem-json-block', {
    onBlock: function (ctx) {
        ctx.content('inner-content');
    }
});
//inner bn
BN.addDecl('mix-use-bem-bn-block').blockTemplate(function (ctx) {
    ctx.content({
        block: 'mix-use-inner-bem-json-block'
    });
}).done();

```