fdo#81475 addition of 'Add Caption' button to table toolbar

Change-Id: I32ea84e4b068158199af5472e576070593ec93ec
Reviewed-on: https://gerrit.libreoffice.org/13621
Reviewed-by: Yousuf Philips <philipz85@hotmail.com>
Tested-by: Yousuf Philips <philipz85@hotmail.com>