New provisioning profile logic

I got tired of creating a commit each time my provisioning profiles
change. Therefore, I wrote a script which handles provisioning for me.

Each time the App Store version of Textual is built, a pre-build script
is ran which scans my Mac for provisioning profiles which match a
specific name. If it finds one that matches, then it creates an
automatically generated xcconfig file which Xcode can read for the
provisioning profile UUID value.

If no provisioning profile is found, then it creates a blank file so
that the file at least exists.