UI tweaks and bugfixes

[ddunc23]

• Filter box should be contained in size and scroll over a certain point - see https://enclosures.memorymapper.org/ for why
• Splash page not closing on mobile
• Colon appears after title on main menu even if there's no subtitle
• 'Reset map' button
• Add setting to change checkboxes to radio buttons for map layers
• Make filter box minimasable
• Handle missing content more gracefully - the map shouldn't go to 404, there should be a 'no data' or similar page when there is content associated with a feature
• Multiple filters are broken on text view - resolve