ERC721 full implementation (#803)

* Rename current ERC721 implementation to BaseERC721

* Implement ERC721 optional & approveAll functionality

* Support for new ERC721 interface

- Tests for new features are pending
- ERC721 is abstract, since it requires metadata implementation
- Move some methods into DeprecatedERC721 contract
- Reorganise base vs full implementation
- Pending tokenByIndex

* Add more tests for ERC721

* Implement suggestions by @dekz

* Update comments in ERC721 contracts

* Implement tokensByIndex extension

- Remove restrictions from mock mint and burn calls

* Add default implementation for metadata URI

This allows token implementation to be non-abstract

* Allow operators to call approve on a token

* Remove gas stipend restriction in call to 721 receiver

* Remove deprecated implementation

We only want to keep the interface, for interacting with already deployed contracts

* Add notice to isContract helper on constract constructors

* Change natspec delimiters for consistency

* Minor linting fixes

* Add constant modifier to ERC721_RECEIVED magic value

* Use 4-params safeTransferFrom for implementing the 3-params overload

* Minor text changes in natspec comments

* Use address(0) instead of 0 or 0x0

* Use if-statements instead of boolean one-liners for clarity

:-(

* Keep ownedTokensCount state var in sync in full ERC721 implementation

* Fix incorrect comparison when burning ERC721 tokens with metadata

* Use address(0) instead of 0 in one more place in ERC721

* Throw when querying balance for the zero address

Required by the spec

* Update links to approved version of EIP721

* Use explicit size for uint

* Remove unneeded internal function in ERC721

Also rename addToken and removeToken for added clarity

* Use underscore instead of 'do' prefix for internal methods in ERC721

* Fix failing test due to events reordering in ERC721 safe transfer

* Fix bug introduced in 74db03ba06

* Remove do prefix for internal setTokenUri method

* Allow transfers to self in ERC721

contracts/token/ERC721/ERC721Basic.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.4.18;
+
+/**
+ * @title ERC721 Non-Fungible Token Standard basic interface
+ * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ */
+contract ERC721Basic {
+  event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
+  event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
+  event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);  
+
+  function balanceOf(address _owner) public view returns (uint256 _balance);
+  function ownerOf(uint256 _tokenId) public view returns (address _owner);
+  function exists(uint256 _tokenId) public view returns (bool _exists);
+  
+  function approve(address _to, uint256 _tokenId) public;
+  function getApproved(uint256 _tokenId) public view returns (address _operator);
+  
+  function setApprovalForAll(address _operator, bool _approved) public;
+  function isApprovedForAll(address _owner, address _operator) public view returns (bool);
+
+  function transferFrom(address _from, address _to, uint256 _tokenId) public;
+  function safeTransferFrom(address _from, address _to, uint256 _tokenId) public;  
+  function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes _data) public;
+}