Support Capture and Authorize in Demo App

[sshropshire]

Summary of changes

• In demo app, either capture or authorize an order based on the original intent
• Related to: https://github.com/paypal/Android-SDK/pull/143

Checklist

~- [ ] Added a changelog entry~

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @sshropshire
• @KunJeongPark