Gitian outputs cleanup

This addresses #5343, and a few things I discussed on IRC with @laanwj. Depends on #5370.

- Tar/zip files before copying to outputs. This fixes symlinks.
- Delete unnecessary files
- Split linux32/linux64 releases
- Split win32/win64 zips
- Post-processing should no longer be required. The deterministic outputs are ready for consumption.

I've updated the release-process notes as best I can without actually doing a real release. I'm sure there are mistakes, but I'm hoping they're minimal.

Because the diff is rough to read, here's the gitian output for all builds (current master):
```
bitcoin-0.9.99.tar.gz (source)
bitcoin-0.9.99-osx.dmg
bitcoin-0.9.99-osx64.tar.gz
bitcoin-0.9.99-linux32.tar.gz
bitcoin-0.9.99-linux64.tar.gz
bitcoin-0.9.99-win32-setup.exe
bitcoin-0.9.99-win32.zip
bitcoin-0.9.99-win64-setup.exe
bitcoin-0.9.99-win64.zip
```
Here's the contents of one of the tarballs. They're all pretty the same with the exception of file extensions and lib semantics:

bitcoin-0.9.99-linux32.tar.gz:
```
bitcoin-0.9.99
├── bin
│   ├── bitcoin-cli
│   ├── bitcoind
│   ├── bitcoin-qt
│   ├── bitcoin-tx
│   ├── test_bitcoin
│   └── test_bitcoin-qt
├── include
│   └── bitcoinconsensus.h
└── lib
    ├── libbitcoinconsensus.so -> libbitcoinconsensus.so.0.0.0
    ├── libbitcoinconsensus.so.0 -> libbitcoinconsensus.so.0.0.0
    └── libbitcoinconsensus.so.0.0.0
```