AI 146237: ADT #1789339: Manifest editor now displays all extra sub-elements.

AI 146237: ADT #1789339: Manifest editor now displays all extra sub-elements.
  Bug description is to add support for <uses-configuration>.
  Currently the Manifest editor already supports <uses-sdk> (which is an
  element node, not an attribute) by exposing it as a manifest attribute.
  That doesn't scale. So instead just provide a tree for all <manifest>
  child elements that are not handled in other pages. Currently that
  contains uses-sdk and uses-configuration but the nice part of it is that
  it will pick up automatically any new manfiest sub elements in the future.
  BUG=1789339

Automated import of CL 146237