Make default search query more useful

Preserve the existing short-circuit behavior for change IDs. OR
together a laundry list of potentially useful predicates in the
default case.

We use the new projects operator for prefix searching on projects,
rather than the hand-rolled substring search previously only found in
this method.

Change-Id: I21bba55e5ff79cd5daa40dd4076f829399164244
4 files changed