Fixed dropdowns on mobile, Flex slider arrows and alert labels in the admin area

Fixed an issue with the dropdown menus in the main navigation. Ref: #1158

Increased the line-height on the flex slider arrows. This fixed an issue with the Flex Slider arrows not displaying correctly. Ref: #1445

Changed all labels in the alert dropdown to positions absolute. This fixed an issue in Firefox where the labels didn't line up. Ref: #1427