package: Create memory buffer only when we need it - if we use parallelism

Otherwise write directly to the resulting zip file.

Change-Id: I75097969f0cccf0b45da591c71221e5ae18668cb
package: Better to use temporary files for huge memory zip streams

ZipPackageBuffer was holding the whole compressed data stream in one
uno::Sequence which seems to be a lot for big documents in some cases.

Change-Id: Ib10d00ac54df9674231f4bbf047fab7e9b0a7d45