Add same-page links to the Module page

The attached patch implements the suggestion. While we wait for #1790280: Module page redesign 2.0 to be completed and committed, perhaps this can be a candidate for back-porting to Drupal 7.x. Here is a screen shot; note that part of the row for File is obscured by the table header, and also note the URL:

Here is a screen shot using the Stark theme.

I have updated the patch now that #1790280: Module page redesign 2.0 has been committed.

One problem: when you jump to an in-page anchor, the desired section is partially obscured by both the table header and the new admin toolbar. We already noticed this in the "Module Page 2.0" issue, comments #174 and #179. I will add #1440628: [Meta] javascript toolbar/tableheader with url fragment mess to the issue summary.

Screen shot (Seven theme): note the URL, that part of the "Field SQL Storage" section is obscured, and that every module in the Requires list and the Required by list is a link.

          $extra['required_by'][] = t('@module (<span class="admin-disabled">disabled</span>)', array('@module' => $files[$required_by]->info['name']));

My version of this line is

          $extra['required_by'][] = '<a href="#' . $page_anchor . '" class="admin-disabled">' . t('@module', array('@module' => $files[$required_by]->info['name'])) . '</a> (<span class="admin-disabled">' . t('disabled') . '</span>)';

I will be happy to rewrite the patch to use the previous style, or to eliminate t() entirely on this line.

Note also that I add the CSS class admin-enabled or admin-disabled (as above) to the links. I do not add any CSS to make use of this, but that can be done at the theme level. The CSS rules in system.admin.css refer to span.admin-enabled and span.admin-disabled, so there should not be any problem with styling the anchors and the "(disabled)" text separately.

Added another link under "Remaining tasks".

I should probably use drupal_html_class() instead of drupal_clean_css_identifier().

If you think the problem of entries being obscured by the admin toolbar and the table header (see the screen shot in #4) is bad enough, then I think a more appropriate status is "postponed". I have noted in the issue summary that #1440628: [Meta] javascript toolbar/tableheader with url fragment mess is blocking this issue.