Re-enabled "…enter image URL on new post form"

RSpec: 806 examples, 0 failures, 11 pending
RuboCop: 186 files inspected, no offenses detected
Re-enabled "Member can publish…view on own page"

RSpec: 806 examples, 0 failures, 10 pending
RuboCop: 186 files inspected, no offenses detected
Re-enabled "…cannot create post without title"

And cleaned up the broken eggs.

* `Actions::CreatePost` was a mess; separated out data filtering and
validation into nested classes. No more ABC complaints!
* Spec for the above needed some fiddling with error messages; because
* `PostsController` finally has complete error messages: "Title must be
present", not "must be present";
* That's also noted in the `PostsController` spec;
* And, finally, the swamp we set out to drain: a feature spec proving
that a member cannot create a post without a title has been re-enabled.

RSpec: 806 examples, 0 failures, 9 pending
RuboCop: 186 files inspected, no offenses detected