Renamed self._plugin -> self.plugin_instance to emphasize it meaning
Testing form data for validity before proceeding.

 This fixes some form data corruption cause by a previous validation error
Multi-Field for 'responsive-heights' is built in class initialization

before it was built in get_form(), but this method is nor available for shared_glossary
It is easier to access the inherited form without @classproperty
Update glossary with content from SharedGlossary model if that exists
Descrease input field widths
Using EXIF orientaion to compute aspect ratio
bas level classes are added to the <img> tag