update gantry to v4.1.5

Release Notes - Gantry Joomla Framework - Version 4.1.5

Bug
• 500 Error in Joomla 3 in some cases
• Cleanup warning on front end Edit.
• Fixed ToTop Feature not triggering the framework behavior correctly
• Custom field ImagePicker won't allow to be used more than once
• Splitmenu for template showing notices
• Dropdown Selectbox responsive menu not rendering
• Backward compatibility with RokRadios
• issue with assigned overrides being used on all pages
• templates layout tab is not keeping changes after close and open of the edit page

Improvement
• Migrate to JInput from JRequest in order to prevent compatibility issues.

Task
• Updated moofx library