Added support for Expo 40 and react-native 0.63

Removed flow types and added traditional PropTypes

Upgrade to getstream@7.1.0

Cleanup around examples

Removed following existing examples:

• example
• examples/one
• native-example

Added new examples:

• examples/expo (Expo 40)
• examples/native (RN 0.63.x)

Replace react-native-image-picker with react-native-image-crop-picker to allow compression.

Fixed pending issues:

• #156
• #154
• #152
• #126
• #99
• #160
• #165

Added compressImageQuality prop on StatusUpdateForm component, which can be used to compress the images before uploading to CDN.