EditPost action now checks for invalid slug.

Cleaning up loose ends. Spec coverage now 100%.

RSpec: 681 examples, 0 failures
RuboCop: 175 files inspected, no offenses detected
UpdatePost action now checks for invalid slug.

Cleaning up loose ends. Spec coverage now 100%.

RSpec: 683 examples, 0 failures
RuboCop: 175 files inspected, no offenses detected
Cleaning up entity-validation ambiguity.

More loose ends. Entities are limited in the amount of validation they
can realistically do without access to the database.

RSpec: 683 examples, 0 failures
RuboCop: 175 files inspected, no offenses detected
More minor cleanup.

Dummy entities never had their #name/#author_name methods called, and
shouldn't in future.

RSpec: 683 examples, 0 failures
RuboCop: 175 files inspected, no offenses detected