Link to views_ui from block settings page.

I put the link into a fieldset. But I don't care much about it.

A link in the other direction could be added from views_ui.

Changes:
- Check access.
- Check if views_ui is enabled.
- Check if view_name or display_id are empty string.

A link in the other direction could be added from views_ui.

This would be a separate issue.

> A minor tweak.

Ok for me to introduce one less local variable.

Looking at the patch again, I think in the current version it will only work for short view names + display names.

In views_block_view():

function views_block_view($delta) {
  // If this is 32, this should be an md5 hash.
  if (strlen($delta) == 32) {
    $hashes = variable_get('views_block_hashes', array());
    if (!empty($hashes[$delta])) {
      $delta = $hashes[$delta];
    }
  }

We need to do the same logic as in views_block_view(), I think.