TPac: non-inherited org unit visibility

TPac: non-inherited org unit visibility

Adds support for displaying org units that are children of hidden org
units in the tpac org unit selector.  A new global flag was added to
control this behavior called "opac.org_unit.non_inheritied_visibility" /
"Org Units Do Not Inherit Visibility".

To avoid confusion / distorted org unit trees, children of hidden org
units are left-padded one less for each hidden parent org unit.  For
example, in the stock org tree, if Sys2 is opac_visible=false (and the
global flag is enabled), the tree in the tpac would appear like so:

Cons
- Sys 1
-- BR1
--- SL1
-- BR2
- BR3
- BR4

Similarly, if CONS was also hidden, the whole tree would be shifted left
by 1 pad depth.

Signed-off-by: Bill Erickson <berick@esilibrary.com>