Update Fixtures

Have fixtures registered in fixture.js so the whole API can be browsed in one location and the request handling logic is separate.

e.g.

/src/models/fixtures/fixture.js

``` javascript
import fixture from 'can/util/fixture/';
import product from './product'; // product request handler

fixture('GET /api/products/{pc5}', product);

export default fixture;
```

/src/models/product

``` javascript
import pc18173 from './products/pc18173';

export default function(request) {
let requestData = request.data || {};

if(requestData.fields) {
let pc18173_reduced = {
pc5: '18173',
colorid: { }
};
let colorid;

for(colorid in pc18173.colorid) {
pc18173_reduced.colorid[colorid] = {
colorid: colorid,
finish: pc18173.colorid[colorid].finish
};
}

return pc18173_reduced;
}
else {
return pc18173;
}
}
```