Add Image Metadata to Image Database

Three new keys:
* artist - Returned parsed text for the artist
* credit - Returned parsed text for credit description
  (e.g. the original source)
* licenseshortname - Short name for the license (e.g. Public domain)

Change-Id: I0abe839a1355b9ac80a3a79899db7980c95f0c0d
Merge "Add Image Metadata to Image Database"
Merge "Update dependencies."
Switch from `when` to `bluebird` for Promise implementation.

Bluebird is very fast.

Change-Id: I7e4718e7b0bd61a774fef1c9dfa7748cd4ab1fce
Switch from `bluebird` to `es6-shim`/`prfun` for Promise implementation.

Use standard ES6 promises.

Change-Id: I1c698ed05453f22b1574aa4e59eef7463f5cec59