Overhaul Emacs packages at the next major version release

[pauby]

The emacs package needs to be overhauled. The package, since version 27.1 has installed the full dependency package and not the 'no-deps' version is claims. Going forward we should use the full dependency package.

See here for explanations about the binaries:

NOTE: From version 28.x onwards, only 64-bit binaries have been released.

• emacs-$VERSION-installer.exe
  Contains a 64-bit build of Emacs with dependencies as an installer package. Mostly, this is the best one to install.
• emacs-$VERSION.zip
  Contains a 64-bit build of Emacs with dependencies. This contains the same files as the installer but as a zip file which some users may prefer.
• emacs-$VERSION-no-deps.zip
  Contains a 64-bit build of Emacs without any dependencies. This may be useful if you wish to install where the dependencies are already available, or if you want the small possible Emacs.

What we need to do is:

• Add an explanation to each package as to what it is and what the difference is to the other packages.
• Create an emacs.portable package that will contain the emacs-$VERSION.zip zip archive. See (emacs.portable) Create a portable Emacs package that is a copy of the emacs package #105
• Create an emacs.install package that will contain the emacs-$VERSION-installer.exe installer. See (emacs.install) Create an Emacs install package #106
• Change the emacs package to a meta package that takes emacs.portable as a dependency. As this package has used the portable method (ie. unzipping the files) up to now it makes sense to keep doing that as it's expected behaviour. See (emacs) Convert to a metapackage depending on emacs.portable #107
• Create an emacs-no-deps package that will contain the emacs-$VERSION-no-deps.zipzip archive. See (emacs-no-deps) Create new package for Emacs with no dependencies #108