gitian: Windows 64 bit support

- Build a 64 bit version of all dependencies
- Show 32/64 bit version in "About..." for x86
- Export 64-bit .exes and installer from gitian build
Adapt Windows installer for 64 bit
build: Add bitcoin-cli.exe to installer
build: Package docs/ and don't package source.

No-one uses the installer then builds from source.
Closes #2819.
build: Change package name to Bitcoin Core

Affects the name of the package as shown in installers
and such.

Also rebrand the windows installer.
Merge pull request #3560

fe14e8d build: Change package name to Bitcoin Core (Wladimir J. van der Laan)
6c980c7 build: Package docs/ and don't package source. (Wladimir J. van der Laan)
39db27c build: Add bitcoin-cli.exe to installer (Wladimir J. van der Laan)
2f87b38 Adapt Windows installer for 64 bit (Wladimir J. van der Laan)
f622232 gitian: Windows 64 bit support (Wladimir J. van der Laan)