Merge pull request #11 from TimBHowe/2.0

• Bug Fix: Removed 'var_dump' in validation function.
• Added 'gf_emailblacklist_clean' function to make comparison case insensitive. Thanks to @ractoon, @rscoates.
• Updated function to work with both email domains and specific emails.
• Ran 'class-gfemailblacklist.php' through PHPCS with WordPress Codeing Standards.
• Moved class to '/inlcudes/class-gfemailblacklist.php' file.
• Added placeholder text to fileds
• Updated code comments.
• Updated plugin file name.
• Updated readme.txt and README.md