doc: Canonical name == App bundle name

There's only one substantive change in this patch, which is
that the Canonical App name is defined exactly by the name
of the App bundle on disk. The suggestion that the author's
website be consulted for orthography is removed.

All but 18 Casks follow this rule already (if we leave aside
version numbers), so that's 98.3% compliance.  I see this change
as documenting the de facto situation more clearly.  The App name
on disk is in any case superior to consulting the website, as it is
less subject to misreading or artistic interpretation.

If this PR is accepted, I will
* rename the remaining variant Casks to follow this rule
* propose a PR to standardize version-numbers-in-names
* propose a PR for name name collisions.

Once the naming rules are fully specified, I'll PR a script which
a Cask author can use to generate the Cask Name and Cask Class
from a given App name, using the same logic as the backend.