Support uploading files to cloudflare

[shiqimei]

1. get presigned upload url from server
2. upload files to cloudflare (event: 'start' | 'progress' | 'success' | 'error')
3. save uploaded url to database

Providers/Adapters

1. default GridFS
2. Cloudflare

external interface

• uploadFile(file: File, callback(event))
• uploadFileWithPreview internally call uploadFile but with extra preview (compressed) image uploaded

[shiqimei]

deprecated