Add Magento's own Mime class to replace usage of Zend_Mime
Zend_Mime package can now be removed.
Also removes call to Zend_Mime_Decode::decodeQuotedPrintable()
Duplicate of magento-engcom/php-7.2-support#102
Contribution checklist
[x] Pull request has a meaningful description of its purpose
[x] All commits are accompanied by meaningful commit messages
[x] All new or changed code is covered with unit/integration tests (if applicable)
[x] All automated tests passed successfully (all builds on Travis CI are green)
Description
Add Magento's own Mime class to replace usage of Zend_Mime Zend_Mime package can now be removed. Also removes call to Zend_Mime_Decode::decodeQuotedPrintable() Duplicate of magento-engcom/php-7.2-support#102
Contribution checklist