New design for approvals settings in merge request form

Bring the design of approvals https://gitlab.com/gitlab-org/gitlab-ee/issues/1738 (that is in the project settings of approvals) to the merge request web form (creating an editing a merge request).
In particular, that is the design to add/remove approvers, and also set the number of approvals required.
This doesn't change any existing functionality of the approvers per merge request. This is just to update the design.
Also include the Suggested Approvers link to be right below the Approvers search box.

Edited Jun 06, 2017 by Filipa Lacerda