Add a "Reply" button to message long-press menu in interleaved views

[alya]

In interleaved views, we should offer a "Reply" button in the message long-press menu. The button should navigate to the conversation view for the message, put focus in the compose box, and open the keyboard.

Decisions to make:

• Label. Possibly, we want something like "Reply to message" or "Reply in conversation", rather than a bare "Reply".
• Icon
• Button position in the list

CZO discussion