Updates to dev_env

[@nnounce]

Features/bugs for latest push to dev_env

@me:
* Security enhancement in authentication flow. 
  User will be prompted to save QR code image. AES key from QR code will be used to secure the key pairs of the user and save the encrypted 
file in phone. (saving to phone storage is a temporary solution. we are working on a solution to store in gdrive/iclouddrive). User has to scan this QR code and reinstallation of the app.
* Profile image upload
  High resolution images will be resized and stored
* other minor bug fixes

@buzz:
* sync metadata
  Metadata such as expiresAt, availableAt will be synced 
* auth flow and profile image upload. Same as @me.
* other minor bug fixes

@client SDK:
* New methods for storing and retrieving binary data
  putBinary and getBinary methods are added to allow storing and retrieving of binary data e.g images. App developers need not worry about encoding and decoding logic. This has been moved to the SDK.
* bug fix in retrieving encrypted data shared with another atSign.

@server:
* Scan bug fix
  keys starting with public:_ will not be shown.