Add Sophos Anti-Virus Home Edition version 9.1p

The current production version of Sophos anti virus is 9.0.X and has a
terrible bug in it related to interfering with CORS requests in Chrome
and Firefox. They have claimed that it is remediated in 9.1, but it is
only in a preview stage right now. If you want to test it out though,
here is the formula to test it.

There is a command line install command for Sophos, but `ditto` was
hanging when unpacking due to a permission within the app bundle itself.
It would be neat if the user wouldn't have to run a separate installer.
For now though, the formula is just modeled after the one currently used
for 9.0.