Code fixes and improvements#201

oleksandr-mykhailenko merged 7 commits intomastermailgun/wordpress-plugin:masterfrom

DE-1443-mailgun-wordpress-php-warning-compact-undefined-variable-cc-and-bccmailgun/wordpress-plugin:DE-1443-mailgun-wordpress-php-warning-compact-undefined-variable-cc-and-bccCopy head branch name to clipboard