Minor tweaks to pre/inline style for inline comments in HTML mail

Summary:
Ref T10694.

• Shift margins/padding around so inlines with multiple paragraphs get reasonable spacing.
• Add text-decoration: none to the "View Inline" link to kill the underline.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10694

Differential Revision: https://secure.phabricator.com/D15863