Highlighting the current day in calendar.

Summary:
Highlights the current day :)
I am not great in choosing colors. @chad can suggest some improvements :)

Test Plan: {F41738}

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin, AnhNhan

Maniphest Tasks: T2627

Differential Revision: https://secure.phabricator.com/D5790