Changes made:

* Rename "Back" to "Reset" like in other dialogs (eg. Writer - Format - Character).
* Apply-Button, which reflects the old behavior of the dialog, and doesn't
  close it automatically.
* Added an OK-Button, which applies the changes made and automatically closes the
  dialog.

With this both use cases should be handled:

* Inserting one single URI with simple close.
* Modifying multiple URIs without closing the dialog.

Hopefully all users are happy with this ;)

Change-Id: I1881dee083945cd165fbb8f8444395c1b04a0607
Reviewed-on: https://gerrit.libreoffice.org/10946Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>