Summary:
Adds a ProgressView component. It displays determinate progress linearly.
Note: the README.md and API has previously been reviewed. Feel free to leave comments, but you can also skip for this review and focus on the implementation.
Test Plan: - Open Catalog > Progress View and verify looks.
Reviewers: randallli, junius, iangordon, O1 Material components iOS, ajsecord
Reviewed By: O1 Material components iOS, ajsecord
Tags: #material_components_ios
Differential Revision: http://codereview.cc/D1103
