Bug fix for content quicktags init

This change prevents mqTranslate from affecting quicktags initialization on editor instances other than "content" (i.e. created by other plugins).
See here for further info: https://wordpress.org/support/topic/mqtranslate-and-black-studio-tiny-mce-update?replies=3
Bug fix for content quicktags init

Additional changes for correct initialization in presence of other editor instances.
Merge pull request #8 from marcochiesi/master

Fixed bug affecting quicktags initialization on editor instances other than "content"