Query to Dropbox API

1. Check error

1.1. Has error

1.1.1. Authentication failed

1.1.1.1. Query OAuth 2.0

1.1.2. Another error

1.1.2.1. Another way

1.2. No error

1.2.1. Get file list

1.2.1.1. Render tree

1.2.1.2. Render gallery