[Design] default attribute values for items created by cosmo

[Brian Moseley]

there are often times that cosmo creates items on its own rather than
having them synced up from chandler:

* an event is uploaded with caldav
* a file is uploaded with webdav
* an event is created in the cosmo ui

when this happens, there are several attributes that are not set:
triage status, triage status changed, last modified by, created on.

should any of these attributes be set by cosmo when creating items? if
so, what rules do we use to set them? when is it important that we
make this happen - 0.6.1 (uses new sharing protocol along with
chandler a5), preview, post-preview?