* Add TimedCrowdsale::_extendTime * Add tests for TimedCrowdsale extending method * Reverse event arguments order * Rename method argument * Refactor TimedCrowdsale test * Simplify TimedCrowdsaleImpl * Fix extendTime method behaviour to deny TimedCrowdsale re-opening after it was ended * Append chengelog * Update CHANGELOG.md Co-Authored-By: k06a <k06aaa@gmail.com> * Update contracts/crowdsale/validation/TimedCrowdsale.sol Co-Authored-By: k06a <k06aaa@gmail.com> * Improve tests