update gantry to v4.1.6

Release Notes - Gantry Joomla Framework - Version 4.1.6

Bug
• Fatal error: Call to a member function getCurrentTemplate()
• parent category missing icon
• issue with assigned overrides being used on all pages
• Notice: Undefined index: responsive-menu
• Selectedsets were rendering with hidden fields if the enabler was disabled
• Issue with base Gantry cache saving override values to cache not just master
• Issue handling deleted template styles still assigned to menu items

New Feature
• Add Mobile Detect library