Bug 7608: Manual history should not always be enabled

Bug 7608: Manual history should not always be enabled

When editing a subscription, the "manual history" block is visible even
if the subscription was created with manual history off.

To test:
1) Create a subscription and do not check the "Manual history" checkbox.
2) Save the subscription.
3) Edit the subscription. Note that the manual history section does not
   appear.
4) Enable manual history. Note the appearance of the manual history
   section.
5) Save the subscription.
6) Edit the subscription. Note that the manual history section appears.
7) Click "[cancel manual history]". Note the disappearance of the manual
   history section, and the unchecking of the "Manual history" checkbox.
8) Sign off on patch.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>