UI/API changes

• CHANGE: Add IPv4/6 toggle to DNS measurement definition in measurement form
• CHANGE: measurement form improved estimate (more precise)
• CHANGE: measurement form changes for traceroute (hide ext header size options if not v6)
• FIX: partial fix for favourite probes not showing (still need to deal with API caching issue)
• FIX: layout issues when toggling menu open/close
• FIX: anchors on coverage page, scrolling
• FIX: formatting of cols for probes/msm listings
• TWEAK: clarify UTC meaning in measurement form timepicker