Merge pull request #13 from drenty/master

Added French translated messages
Updated messages
Updates as per Yii2 coding style
Modified keyboard messages
Modified keyboard messages
Export as text/html enhanced for all browsers
Reformatted as per Yii2 coding standards
Fix #14: Export form rendering correction
Fix #14: Hide export form fields
Composer dependency updated
Success and error validation styles
Fix #16: Export form submission enhanced
Fix #16: Revamped export form and iframe
Markdown export enhancement for full screen