[FIX] crm, hr_recruitment, task, issue: fixed default priorities + order based on priority (desc for everyone now)
[IMP] models: move prefetching of records back to method _prefetch_field

The selection of records in cache for prefetching was moved to method
_read_from_database() by xmo at rev 785018cc in order to fix an access right
bug.  But this introduced an issue: to explicitly avoid prefetching, you should
use read() instead of browsing records.  We revert the change by xmo, without
reintroducing the bug (which apparently was fixed by another way).