Upgraded to RN 0.60.5

[markmadlangbayan]

I tried to use the existing PR, but there were issues. It was using the ListView's DataSource, and feeding it to FlatList's data property. I tried, but I was just getting a blank modal screen. After attempting to fix it, I came up with a totally different solution.

These are the changes:

• Completely migrated to FlatList without using any deprecated ListView code.
• Removed warning suppression about ListView
• Fixed warnings
  • Used getDerivedStateFromProps() instead of componentWillReceiveProps(); causing blank modal.
  • Fixed warning about “VirtualizedList: missing keys for items, make sure to specify a key property on each item or provide a custom keyExtractor.” by specifying keyExtractor.
  • Changed package.json from dependencies to peerDependencies. It was causing ambiguous errors about React when trying to develop.
  • Updated React version that's compatible with 0.60.5.
• Replaced example and replaced it with default template from 0.60.5 and then copied over the example from App.js.
• Modified the example to write to the console instead of alert. It was throwing an error about Window Hierarchy. This might be some sort of race condition when the modal is trying to dismiss and at the same time an alert is being shown. Sometimes it will display the alert, but just make the whole screen unresponsive. I think it maybe be covering the alert box by the Modal. Anyway, it may not be part of the actual library itself.
• Just minor typo in example (Custome).