[Support] Added "demo_users" Rake task.

No app- or spec-level code affected.

RSpec: 767 examples, 0 failures (but see Issue #87)
RuboCop: 152 files inspected, no offenses detected
Progress. Only feature specs break.

The main news is the PostCreatorAndPublisher and BlogPostAdder DSOs
respecting draft/public status.

RSpec: 788 examples, 11 failures (but see Issue #87)
RuboCop: 154 files inspected, no offenses detected
Clean specs, FUGLY fix.

Far too much ceremony in `PostsController#create`. Previous use of
`post_status` item in `params` hash to PostCreatorAndPublisher DSO now
looks better in practice than the current, separate parameter. Oh,
well. Later.

RSpec: 788 examples, 0 failures (but see Issue #87)
RuboCop: 154 files inspected, no offenses detected
Updated PostCreatorData to support post status.

Initial status may be set using the hash passed to #initialize; the
#step method (which sets body and title to the next in the sequence)
now accepts a status string for the "new post".

RSpec: 804 examples, 0 failures (but see Issue #87)
RuboCop: 154 files inspected, no offenses detected
FeatureSpecNewPostHelper updated.

`FeatureSpecNewPostHelper#fill_in_new_post_form` no longer forces all
articles to be `public`, but honours the setting passed in from the
initialiser's `data` parameter and/or the value passed to `#step`.

RSpec: 804 examples, 0 failures (but see Issue #87)
RuboCop: 154 files inspected, no offenses detected
PostDataDecorator#pubdate_str works with drafts.

When `#pubdate_str` is called on a published post, it returns a
timestamp string, as before. Now, when called on a draft post, it
returns the string 'DRAFT'.

RSpec: 805 examples, 0 failures (but see Issue #87)
RuboCop: 154 files inspected, no offenses detected
Added first "create draft post" feature spec.

RSpec: 807 examples, 0 failures (but see Issue #87)
RuboCop: 155 files inspected, no offenses detected
"Create draft post & navigate to it" feature spec.

RSpec: 807 examples, 0 failures (but see Issue #87)
RuboCop: 155 files inspected, no offenses detected
Index page now shows draft posts in listing.

To do this, reworked `BlogHelper#summarise_blog` with new
`BlogHelper::BlogSummariser` class. Also added feature spec proving
that a post author can create a draft post and see it in the index page.

Now to prevent anyone *else* from seeing it there.

RSpec: 816 examples, 0 failures (but see Issue #87)
RuboCop: 158 files inspected, no offenses detected
Direct nav to draft articles now prohibited.

Except to their author, of course. Also changed PostsController spec
for "GET ':show'" action to test public posts, draft posts by the
currently logged-in user, and draft posts by a different user.

RSpec: 828 examples, 0 failures (but see Issue #87)
RuboCop: 158 files inspected, no offenses detected
Added new feature spec per last commit

A draft post is only directly navigable/accessible to its author, and
other registered users and the guest user are proven to be blocked.

RSpec: 831 examples, 0 failures (but see Issue #87)
RuboCop: 159 files inspected, no offenses detected
Draft post only visible in profile to author.

This required *significant* change to UsersHelper support class
ProfileArticleListBuilder, which was just going and grabbing all
PostData records authored by a particular user.

RSpec: 834 examples, 0 failures (but see Issue #87)
RuboCop: 161 files inspected, no offenses detected
Merge pull request #107 from jdickey/issue-52-case-3

Issue #52 Use Cases 3-5 now implemented.