Adding comment field to Journal expanded entry

This series of patches adds a new box for comments to the detail view of the
Journal. The box appears below the Tags box and above the Buddy
list. The comments are retrieved from the comments metadata file, if
it is present. The format of the comments metadata file is a
json-encoded list of dictionaries, one for each comment. The
dictionaries contain three optional fields: "from", "message", and
"icon". There is also a mechanism for deleting the comments.

The comments metadata is used by the Portfolio activity (when shared,
comments can be added to portfolio entries). It is also available to
web services, which allow comments on shared content.

The feature page associated with these patches is found at [1].

The first two patches are staging. In 0001, I modify _create_scrolled such that it can accept more than one widget type. In 0002, I move the code for writing the entry to the datastore to a separate method so that it can be called from multiple places.

The third patch, 0003, creates a new width for the comments.

The fourth patch, 0004, adds this widget to the expanded entry and provides external methods for updating this view.

[1] http://wiki.sugarlabs.org/go/Features/Comment_box_in_journal_detail_view