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

Example:

Order
+ id
+ customerName
+ List 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";
```