Add appcast stanzas for 187 `latest`-style Casks

The `appcast` stanza has been supported by the DSL for some time, though
we aren't doing anything with it (yet).

For Casks using the `latest` schema, the content available at the appcast URL
contains a version-specific URL which may be a preferable alternative.

Appcasts can be used for automated detection of available updates. I have a private
snapshot of appcast content from 3 March which I intend to compare against recent
fetches for these Casks.

The appcast URLs in this PR are not a complete set.  They were extracted only for
the following subset
 - Cask uses the `link` artifact to install an App bundle
 - Casks uses the `version 'latest'` schema
 - Application uses Sparkle for appcasting, in the default form (`SUFeedURL` key readable from `Info.plist`)

@alebcay, I thought you might be interested in incorporating appcast changes into
your nightly Cask check.