Add isExplicitUpload to true on macro uploads

Summary: Fixes T3798. Macros now show up as manually uploaded

Test Plan: Upload a macro, go to file, new macro is visiable

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T3798

Differential Revision: https://secure.phabricator.com/D6887