Bug 11605: fallback to default DataTables settings where possible

The default entry is 20 and can be apply to all tables.

Bug 11555 apply the menu entries to all tables, redefining it is
uesless and can be removed.

Test plan:
Test pages impacted by this patch and verify there is no regression on
the tables.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit bb96da8ff86798df099a99e3123796731659fb67)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Bug 11605: (follow-up) fix regression

Bug 11314 overrides the iDisplayLength and aLengthMenu values and should
be kept.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit e2ef2f51d03f31b45396a88529a46af35b0b08e3)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>