Make calendar day view events fill up the correctly sized slots

Summary: Ref T4393, Make calendar day view events fill up the correctly sized slots. (not handling overlapping slots)

Test Plan: Create an event 4:30-5:30am. Day view should correctly reflect when event happens.

Reviewers: epriestley, #blessed_reviewers, chad

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T4393

Differential Revision: https://secure.phabricator.com/D12700