ZlibCompressor: Allow setting the compression level
Allow specifying the compression level for package creation

* Introduce BPackageWriterParameters which comprises all parameters
  for package creation, currently flags and compression level. Such an
  object can be passed to BPackageWriter::Init() and is passed on to
  PackageWriterImpl and WriterImplBase.
* PackageFileHeapWriter: Add compressionLevel property and pass the
  value on to ZlibCompressor.
* package add/create: Add options -0 ... -9 to specify the compression
  level to be used.
Add HAIKU_PACKAGE_COMPRESSION_LEVEL build variable

It allows to control the compression level used for package creation
and update. The default (9) is *very* slow, so developers may want to
use a smaller level during the regular development process to keep
turn-around times low.