Cleanup search placeholder black/gray text mess

Document all these cryptic selectors
Drop -webkit support - not necessary
Follow up to: Ief9a5a178058eb01ab032cfae8639b0fc52c47a4
Note: For the record, I think all these rules should die
but if they are not going to they should at least be documented!
Change-Id: I3bb2d9fc4f8502cbf36356a9bc6e3034d2d47ab1