[453173] Reduce consumed memory by DBStore

Have ObjectTypeTable reset its field on deactivation.
Have DBField store Exception only when DBIndex.DISABLE_NULLABLE_CHECK
and DBIndex.FIX_NULLABLE_INDEX_COLUMNS are at false to limit comsumed
memory of DBField.

Change-Id: If1a0b11e0405bcefdf0d73ff42b21f97fe8c7ca7
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=453173
Signed-off-by: Esteban Dugueperoux <esteban.dugueperoux@obeo.fr>