Improve Menus and Title Names to Better Match Content

[joshjacobson]

• Rename the menu item "Mitigation" to "Mitigation Calculator" (capitalization changes are intentional)
• Rename the menu item "Mitigation Scenarios" to "Country Scenarios"
• Rename the menu item "Mitigation Map" to "Global Rt Map"
• Rename the menu item "Models" to "Country Rt Estimates"
• Rename the menu item "Request a model" to "Submit a Request"
• Change the text at the top of the page that will now be titled "Mitigation Calculator" from "MITIGATION CALCULATOR" to "MITIGATION CALCULATOR FOR POLICYMAKERS"
• Move the menu item now called "Mitigation Calculator" to the first menu position
• Change the "logo" text in the upper left to "EPIDEMIC FORECASTING: COVID-19"