Add page to admin ui for viewing a topical event

Each event has a couple of tabs - Details and Features. Direct links to
the edit page and "featured items" page have been removed from the
/government/admin/topical-events page.
Add model_name helper to Admin::ClassificationsController
Always wrap count of published policy/guides

The number of polices/detailed guides is made much easier to scan and
cmopare for multiple topics/topical events when the figures are left
aligned, rather than being presented in a single sentence.
Simplify names of nouns in Cucumber steps

Features or tests that are full of irreverent names are fun, but
obfuscate the intent of the test. When the names are long they tend to
dominate the text, making the intended behaviour hard to tease out.

And the more text you have to read, the more brain power you need to
dedicate to parsing it, rather than understanding it.
Tidy up topical events index page

- Dropped the 'view' and 'featured items' links (will be accessible from
  each topical event's page)
- Truncated the event's copy (in the description column) to the first
  130 characters.
Make human_friendly_model_name a helper method
Consistent page layout on Topical Events tab pages
Use <th> tags for table headings
Add 'Read more' tab to Topical Events admin pages
Move 'Read more' admin pages to AboutPagesController
Create AboutPage for topical events from admin UI
Add name of topical events About page to summary in admin UI
Edit and update About pages for topical events
Fix URL for creating about pages
Show govspeak when editing pages about topical events
Link to about page from topical event
Display page of copy about a topical event on public site
Make topical event about pages searchable
Render Markdown for about page body in admin UI
Select Topics in main nav when on About page