Fix SafeERC20.safeApprove bug

(cherry picked from commit 3111291b)

* Made _clearApproval private, added clarifying comments in _addTokenTo and _removeTokenFrom.

* Added approval information.

(cherry picked from commit 8204f6a7)

This attack was reported in https://github.com/OpenZeppelin/openzeppelin-solidity/issues/877

(cherry picked from commit 80458ebc)

(cherry picked from commit 6d415c50)

(cherry picked from commit a936cbf5)

(cherry picked from commit 1ac1ac98)

* Deleted unnecessary import.

* Added back SafeMath.

* Removed another unnecessary import.

(cherry picked from commit bbe804a1)

Now setting the finalized flag before doing finalization to prevent possbile reentrancy issues. (#1447)


(cherry picked from commit 5bb86521)

* Added a small Crowdsale fallback gas warning.

* Fixed a couple typos.

(cherry picked from commit 94692acb)

(cherry picked from commit 384dff9a)

(cherry picked from commit 5bf39078)

(cherry picked from commit c8220aee)

(cherry picked from commit 9155bfe2)

(cherry picked from commit 1c5f16ae)

* Made some internal crowdsale methods internal.

* Made all Crowdsale constructors internal.

(cherry picked from commit d9fdffe8)

* signing prefix added

* Minor improvement

* Tests changed

* Successfully tested

* Minor improvements

* Minor improvements

* Revert "Dangling commas are now required. (#1359)"

This reverts commit a6889776.

* updates

* fixes #1404

* approve failing test

* suggested changes done

* ISafeERC20 removed

* allowance methods in library

* Improved SafeERC20 tests.

* Fixed test coverage.

(cherry picked from commit 315f426f)

* Improved TokenVesting events.

* Added extra checks to TokenVesting.

* Renamed the events.

* Fixed linter error.

* Fixed a test that failed to cover a require.

* Renamed TokensRevoked to TokenVestingRevoked.

(cherry picked from commit 67dac7ae)

* Renamed file, added events and set _addPayee to private

* unwanted file

* adjusted test

* adjusted test

* PaymentReceived event added

* Added event testing.

* Fix static tests

(cherry picked from commit a0749979)

* Added address of pauser/unpauser in events

* Added the account to the Pausable tests.

(cherry picked from commit fcab9c89)

* Update contracts/ownership/Secondary.sol

* Update Secondary.sol

* Update Secondary.test.js

* Update Secondary.test.js

* Update Secondary.sol

(cherry picked from commit cbe41486)

(cherry picked from commit 0231fac5)

(cherry picked from commit ff0c048a)

* Made some inherit-only contracts internal.

* Added OwnableMock.

(cherry picked from commit 96d6103e)

* Made some TokenVesting public functions private.

* Fixed linter error.

(cherry picked from commit df3c1137)

* Moved Escrows into an escrow subdirectory, improved docs.

* Fixed escrow mock.

* Fixed some more imports.

(cherry picked from commit f3df2dab)

(cherry picked from commit cfef5836)

(cherry picked from commit d8ab8a00)

(cherry picked from commit 2733cb4a)

* added function to renounce ownership

* Make state variables private (#1411)

(cherry picked from commit 03765e08)

(cherry picked from commit a3e312d1)

(cherry picked from commit 3341dd88)

(cherry picked from commit 3bd30f73)

* fixes #1414

(cherry picked from commit 844a96d0)

* use prefix underscore for internal state variables

* make _supportedInterfaces private

(cherry picked from commit 03dfb296)

* Removed unused advanceToBlock.

* Added advanceBlock tests.

* Fixed advanceToBlock tests.

* Added single argument tests.

* Finished inLogs tests.

* Fixed linter errors.

* Fixed linter errors.

(cherry picked from commit 9f822906)

(cherry picked from commit eb92fd1f)