[PATCH v3] clip: add option PASSWORD_STORE_PASTE_ONCE

[grmat]

Personally, I've never considered PASSWORD_STORE_CLIP_TIME very useful,
so my opinion on this might be irrelevant. Before I added --paste-once I
used to clear it manually right after I pasted it, so I never ran into
the timeout.

However I would assume that users who appreciate this feature wouldn't
want it go away implicitly by enabling PASTE_ONCE.
Scenario: enable PASTE_ONCE, but don't actually paste because you got
something else to do, will remain in clipboard "forever" and might be
pasted unintentionally somewhere else.