R1:2c03cd931bd2

Legalpad V0.2 - add mail integration

Summary:
Supports !unsubscribe and commenting on replies. Subscribers get mailed something reasonable. Fixes T3480.

Sneaks in /LX/ support. In the near future I want to have that /LX/ be a clean "signature" page sans all the edit actions and other fluff... Will resolve this as part of T3481.

Test Plan: used the metamta console to add comments and unsubscribe. added a phlog() inside mail code to verify mail bodies looked okay.

Reviewers: epriestley

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