Use new application icons and intended side nav icons

Summary: @chad, can you do the icon sheets based on 1.6? We're using a few icons not present in 1.5. I put the 1.6 "pro" source on Dropbox.

Test Plan:
Nav hover and selected states:

{F20598}

Launch hover state:

{F20596}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1856

Differential Revision: https://secure.phabricator.com/D3649