Fix #379: change Pagination links to spans; avoid IE9+ dispatchEvent bug

This led to a few other changes as a result, to ensure equivalent
functionality as before:

* Added "dgrid-page-link" class to all clickable nodes in the navigation area
* Added tabIndex to all nodes that were formerly `a` tags, so that they are
  still keyboard-navigable
* Added keyboard handling to all nodes that were formerly `a` tags, so that
  enter still fires their actions
* Removed IE<8 CSS that is no longer needed
Document Pagination changes for IE9+ dispatchEvent fix in CHANGES.md