Change: move permission cache to dedicated files

[mattmundell]

What

Move the permission cache code out of manage_sql.c.

Why

Next step in reducing size of manage_sql.c.

References

Follows /pull/2745 for permissions.

Testing

  cache_permissions_for_resource
    clone task, cache count incr
  cache_all_permissions_for_users
    --optimize rebuild-permissions-cache, watch cache count incr
  delete_permissions_cache_for_resource
    ultimate del task, cache count decr
  delete_permissions_cache_for_user
    rm user, cach count desr