Make similar/subtask actions clickable

Summary: Adding better CSS and set correct tag and examples.

Test Plan: Test UIExamples, creating and click on similar task, empty task in Maniphest.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7423

Differential Revision: https://secure.phabricator.com/D11932