Support kcfinder image upload

Many thanks @dsnopek for writing this plugin!

There are two related changes happening in this MR.

The first is that I'm copying kcfinder to <cmsroot>/web/libraries/civicrm. I think that's uncontroversial, owing to these two lines.

Secondly, I'm changing settings_location.php to an absolute path. However, I think this might need discussion, since I think it speaks to a difference in configuration. Your relative path assumes that civicrm.settings.php is in <webroot>/sites, but mine is in <webroot>/web/sites/default. Without this change, kcfinder can't find civicrm.settings.php.

Finally, please note that to test this successfully, you also need to apply a patch from Drupal#42.