ERC20 compatibility of Amp token using defaultPartition
It is somewhat unclear how the Amp token ensures ERC20 compatibility. While the `default` partition is used in some places (for instance, in function balanceOf) there are also separate fields for (aggregated) balances/allowances. This seems to introduce some redundancy and raises certain questions about when which fields are relevant.\\n`_allowed` is used in function `allowance` instead of `_allowedByPartition` with the default partition\\nAn `Approval` event should be emitted when approving the default partition\\n```\\nemit ApprovalByPartition(\\_partition, \\_tokenHolder, \\_spender, \\_amount);\\n```\\n\\n`increaseAllowance()` vs. `increaseAllowanceByPartition()`
After the mid-audit discussion, it was clear that the general `balanceOf` method (with no partition) is not needed and can be replaced with a `balanceOf` function that returns balance of the default partition, similarly for allowance, the general `increaseAllowance` function can simply call `increaseAllowanceByPartition` using default partition (same for decreaseAllowance).
```\\nemit ApprovalByPartition(\\_partition, \\_tokenHolder, \\_spender, \\_amount);\\n```\\n