Tidy up global capability definitions

Move MODIFY_ACCOUNT to correct alphabetical order.

Rename DEFAULT_MAX_BATCH_CHANGES to DEFAULT_MAX_BATCH_CHANGES_LIMIT,
and move it up so it's right after BATCH_CHANGES_LIMIT. This makes it
consistent with the way DEFAULT_MAX_QUERY_LIMIT is defined.

Change-Id: Ie71a7a5886f95a50e9dae25ba16b3717e2ce27a7