Create a plugin that generates a constants file with parameter names per-generated class

Example:

Order
 + id
 + customerName
 + List<Items> items

Item
 + id
 + sku
 + cost


Generates:

OrderFields.java:
```
public static final ID = "id";
public static final CUSTOMERNAME = "customerName";
public static final ITEMS = "items";
```

ItemFields.java:
```
public static final ID = "id";
public static final SKU = "sku";
public static final COST = "cost";
```