Formula, Cask: add livecheck_defined hash value

The `Tap.autobump` logic was recently updated to not skip deprecated
packages but this has lead to autobump checking packages that
livecheck will automatically skip as deprecated. We want autobump to
only check deprecated packages that are checkable and that effectively
means only checking those with a `livecheck` block. To be able to do
this, we need to include the `livecheck_defined?` value in the JSON
API data for formulae and casks.

This adds a `livecheck_defined` value to `Cask#to_h` and
`Formula#to_hash` as a preliminary step. We need to add this value and
for it to be present in the latest JSON API data before we can use it
in `Tap.autobump`.