Modernized Phriction Document Index

Summary:
Refs T2686

Migrated Document Index to PhabricatorObjectItemView

Updates page currently depicts change type per object bar color. Icons are planned, though their implemention remains unclear.

Also, @btrahan mentioned the use of getters over properties (for $this->documents, $this->handles)

Test Plan: Looks good, doesn't it?

Reviewers: epriestley, chad, btrahan

CC: aran, Korvin

Maniphest Tasks: T2686

Differential Revision: https://secure.phabricator.com/D5403