* Error handling in ERC20 and ERC721 * Added message string for require. * Fixed solhint errors. * Updated PR as per issue #1709 * changes as per #1709 and openzeppelin forum. * Changes in require statement * Changes in require statement * build pipeline fix * Changes as per @nventuro's comment. * Update revert reason strings. * Fianal update of revert reason strings. * WIP: Updating reason strings in test cases * WIP: Added changes to ERC20 and ERC721 * Fixes linting errors in *.tes.js files * Achieved 100% code coverage * Updated the test cases with shouldFail.reverting.withMessage() * Fix package-lock. * address review comments * fix linter issues * fix remaining revert reasons