Add inline comments to Diffusion/Audit

Summary:

• Add inline comments to Audits, like Differential.
• Creates new storage for the comments in the Audits database.
• Creates a new PhabricatorAuditInlineComment class, similar to DifferentialInlineComment.
• Defines an Interface which Differential and Audit comments conform to.
• Makes consumers of DifferentialInlineComments consume objects which implement that interface instead.
• Adds save

• Inline comments aren't shown in the main comment list.
• Inline comments aren't shown in the emails.
• Inline comments aren't previewed.

I'll followup with those but this was getting pretty big.

@vrana, does the SQL change look correct?

Test Plan:

• Created, edited, deleted, replied to, reloaded and saved inline comments in Diffusion, on the left and right side of diffs.
• Created, edited, deleted, replied to, reloaded and saved inline comments in Differentila, on the left and right side of primary and diff-versus-diff diffs.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T904

Differential Revision: https://secure.phabricator.com/D1898