Make a less fancy difficulty filter in SelectRoute/Trails

[kachnitel]

Need to drop multi-slider to upgrade to SDK 36 (#104)

Make it more obvious to use

• Show 'Tap here to filter' text if no filter is set
  • Show small preview of current filter
• Tapping opens a modal with options and close
  • SelectDifficulty / SelectWithIcon do not support selecting multiple being react-native-custom-picker based
  • Create a Filter modal (see SetPrivacy but better...)