(Bug 5286) Darken Light Gray Text on Foundation Pages

Lynx:

Set $_dark-gray to #636363, name this $secondary-color, then define
$sub-nav-font-color and $pagination-link-font-color and
$pagination-unavailable-link-font-color to be this color.

Note: The white on blue for active Pagination and Sub Nav links
fails AAA for Normal Text. Not fixed as part of this bug.

Celerity:
Changes $_dark-gray to $_mid-gray and defines $_dark-gray as
color to $sub-nav-font-color and $pagination-link-font-color and
$pagination-unavailable-link-font-color using intermediate variables
$sub-nav-color and $pagination-font-color.

Gradation:
No changes made.

Note: $sub-nav-active-bg (set to $primary-color) fails contrast
check for white text. Not fixed as part of this bug.