Added basic Packager application

Summary:
Refs T176

Adds a basic Packager application to Phabricator.

You can add and edit packages by providing links to the files located on Amazon S3. You can also download these files, as it is capable of providing you short-lived download links.

Download tracking is being added in the future.

Test Plan:
fiddled around with it - a lot

= Screenshots =

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Reviewers: anh-chrome

Reviewed By: anh-chrome

Maniphest Tasks: T176

Differential Revision: http://phabricator.burningreality.de/D120