Remove subunitLink class from HTML and CSS

Within the div element with subunitLinks ID, there are div
elements with subunitLink class. Remove subunitLink class from
HTML and CSS. Let the div element with subunitLinks contain
plain div elements. Accordingly, change the '.subunitLink'
selector in CSS to '#subunitLinks div'.
Remove thin gray box that appears if there are no subunits

When there are no subunits within the div element with
subunitLinks class, a small gray box appears for the div element
with .stretch class due to two issues:

  1. The 'width: 19%' property in '#subunitLinks div' overrides
     'width: 100%' property in '.stretch'.
  2. The 'border' property in '#subunitLinks div' creates a thin
     gray border.

We want the width of the div element with .stretch class to be
100% while the div element itself should be completely
invisible. Fix this by increasing the specificity of the
selector of this element from '.stretch' to
'#unitLinks div.stretch'. Remove the gray box by explicitly
defining 'border: 0' property for the selector of this element.
Dynamically generate subunit links from units.js

The subunit links are currently static div elements in HTML.
Remove these static div elements from HTML. Generate these links
dynamically for Unit 1 only.

Ensure that the function that generates the links dynamically
accepts an integer argument with which the unit number for which
the subunit links are to be generated can be specified. Invoke
this function for Unit 1 at this time.