The current TAB-ing order of Gallery sidebar panel is not sequential
and the order needed to be changed. This patch fixes the TAB-ing order
of the gallery sidebar panel to a more sequential and convenient one.
It also fixes the reverse TAB-ing order (Shift+TAB).

Change-Id: Ib0b22ccef1fa4676e535f42a794fb7c836741d0b
Reviewed-on: https://gerrit.libreoffice.org/65907Reviewed-by: Jim Raykowski <raykowj@gmail.com>
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>