Gov notice and Challenge header with Logged In and Logged out states …

[jairoanaya]

…- on eval branch.

Description

Added Gov Notice Header and Challenge.gov header.

Related Issues

None

Changes Made

Added new images
Added template _govheader.html.eex
Modified root, app and head layaout.

Screenshots (if applicable)

See #1362

Checklist

• PR is assigned to a project: Challenge_gov Board
• PR is assigned to a milestone: current sprint
• GH issues are assigned to the PR (under Development section on the right hand side)
• PR is assigned a reviewer, and requires code review and approval by a teammate
• New functionality is tested and all tests are green
• I have added unit tests for new functionality or updated existing tests for changes.
• I have updated the documentation/README accordingly, if necessary.
• If you have DB migration, it is a "safe" migration and you've confirmed it can be rolled back.
• If applicable, Controllers modified contain appropriate authorization plugs
• This PR has been reviewed by at least one other team member.