Bug 846740 - Move most l10n-repack code under mozpack.packager, refactor it, and add a unit test. r=gps

--HG--
rename : toolkit/mozapps/installer/l10n-repack.py => python/mozbuild/mozpack/packager/l10n.py
Bug 846740 - Treat chrome searchplugins as non-chrome when doing l10n-repack. r=gps
Bug 847479 - Add buffer length information when initializing a SeekableZStream. r=nfroyd
Bug 847479 - Add a helper class for a buffer mapped from a file. r=nfroyd
Bug 847479 - Add a command line argument to szip to decompress an existing seekable stream. r=nfroyd
Bug 847479 - Sanity check that szip's compressed output can properly be decompressed. r=nfroyd
Bug 847479 - Use raw zlib streams when compressing with szip. r=nfroyd

And keep compatibility to decompress old streams.
Bug 847479 - Allow to specify a chunk size on szip command line. r=nfroyd
Bug 847479 - Add smart filters borrowed from xz-utils to improve SeekableZStream compression rate. r=nfroyd
Bug 847479 - Add a dictionary to improve compression rate. r=nfroyd