add newlines to header.php html output

[simonLeary42]

introduced in #385

before:

  <nav class="mainNav">
    <a href='http://127.0.0.1:8000/index.php'>Home</a><a target='_blank' href='https://github.com/'>Global Menuitem 1</a><a href='http://127.0.0.1:8000/panel/support.php'>Support</a><a href='http://127.0.0.1:8000/panel/account.php'>Account Settings</a><a href='http://127.0.0.1:8000/panel/groups.php'>My PIs</a><a href='http://127.0.0.1:8000/panel/pi.php'>My Users</a><a target='_blank' href='https://github.com/'>Secure Menuitem 1</a><hr class='navHR'><a href='http://127.0.0.1:8000/admin/user-mgmt.php'>User Management</a><a href='http://127.0.0.1:8000/admin/pi-mgmt.php'>PI Management</a><a href='http://127.0.0.1:8000/admin/notices.php'>Cluster Notices</a><a href='http://127.0.0.1:8000/admin/content.php'>Content Management</a>  </nav>

after:

  <nav class="mainNav">
    <a href='http://127.0.0.1:8000/index.php'>Home</a>
<a target='_blank' href='https://github.com/'>Global Menuitem 1</a>
<a href='http://127.0.0.1:8000/panel/support.php'>Support</a>
<a href='http://127.0.0.1:8000/panel/account.php'>Account Settings</a>
<a href='http://127.0.0.1:8000/panel/groups.php'>My PIs</a>
<a href='http://127.0.0.1:8000/panel/pi.php'>My Users</a>
<a target='_blank' href='https://github.com/'>Secure Menuitem 1</a>
<hr class='navHR'><a href='http://127.0.0.1:8000/admin/user-mgmt.php'>User Management</a>
<a href='http://127.0.0.1:8000/admin/pi-mgmt.php'>PI Management</a>
<a href='http://127.0.0.1:8000/admin/notices.php'>Cluster Notices</a>
<a href='http://127.0.0.1:8000/admin/content.php'>Content Management</a>
  </nav>