- Refactor assetWrapper to contain more of the normalizing logic instead of erc20Wrapper and erc721Wrapper

- Add burn method to DummyERC721Token
- Add additional methods to assetWrapper to set balance/allowances on ERC20 and ERC721 tokens
- Use approve instead of approveAll for ERC721 tokens

packages/contracts/test/asset_proxy/proxies.ts

@@ -473,7 +473,8 @@ describe('Asset Transfer Proxies', () => {
                     txHash,
                     constants.AWAIT_TRANSACTION_MINED_MS,
                 );
-                expect(res.logs.length).to.equal(numTransfers);
+                const numApproveEvents = 2;
+                expect(res.logs.length).to.equal(numTransfers + numApproveEvents);
 
                 const newOwnerMakerAssetA = await erc721Token.ownerOf.callAsync(makerTokenIdA);
                 const newOwnerMakerAssetB = await erc721Token.ownerOf.callAsync(makerTokenIdB);