Add the new site-header template for the DotOrg design

[amieiro]

This PR implements the new design for the site-header at translate.wordpress.org, using only blocks. This PR:

• Adds a new site-header template in the new design.
  • Adds the global-header block.
  • Adds a hard-coded menu.
  • Adds some inline CSS, copied from other site at wordpress.org, that should be removed in a future PR.
• Removes the call to the gp_tmpl_header(); method.
• Adds the new header and footer in the new-design. We need to iterate in these templates.

Currently, this PR only works in My events, because we don't have another main templates in the new design.

New design with the current template system

New design with blocks

Currently, we have a problem with the breadcrumb at translate.wordpress.org, because it is not working. We should address this problem in a future PR.

[psrpinto]

Merging, we can iterate in future PRs.