Rowel

## What's Changed
* feat(identity): ask which document in the add picker, not from a switch inside the form by @alchaplinsky in https://github.com/fwdai/rowel/pull/616
* fix(scan): keep a mangled MRZ from being read as a card by @alchaplinsky in https://github.com/fwdai/rowel/pull/617
* docs(banner): Update readme.md and banner by @alchaplinsky in https://github.com/fwdai/rowel/pull/618
* Mask secrets with the brand asterisk instead of dots by @alchaplinsky in https://github.com/fwdai/rowel/pull/620
* Update Readme.md by @alchaplinsky in https://github.com/fwdai/rowel/pull/621
* refactor(sync): provider-neutral sync core with Google Drive as the first adapter by @alchaplinsky in https://github.com/fwdai/rowel/pull/592
* feat(sync): Dropbox as a sync provider by @alchaplinsky in https://github.com/fwdai/rowel/pull/593
* feat(sync): provider picker and provider-neutral naming by @alchaplinsky in https://github.com/fwdai/rowel/pull/594
* fix(sync): review findings: Dropbox compare-and-swap, disconnect under the lock, cancelled sign-ins free their port by @alchaplinsky in https://github.com/fwdai/rowel/pull/595
* feat(sync): iCloud as a third provider, through CloudKit by @al