Add category dropdown with filtering and nearest to me dropdown on SRP

[shadforth]

High-level overview

• Add dropdowns to SearchResultsPage and with react-native-picker-select library
• Add useState hook to filter items
• Add filteredBusinesses in order to keep businesses in tact - this could be better
• Add FontAwesome for dropdown chevrons, with guidance from Jolly
• Fix up some styles on the DiscoverScreen after moving onPress() to <TouchableOpacity>
• Clean up some styles here and there

Callouts

• No logic or filtering applied to 'nearest to me' dropdown yet
• Ideally, have dropdown chevron animating by rotating 180 degrees on activation
• Still need to handle selecting 'All categories' again

Preview

Resources

• react-native-picker-select
• react-native-fontawesome