On local builds we shouldn't upload errors to Sentry. The
`build-utils.sh` script sets the `UPLOAD_SENTRY` environment variable
for that purpose. Also, Sentry doesn't like having an empty string
as pkgversion (which should no longer happen with the rest of this
change, but...)
This change adds a virtual package `keyman-engine` which ibus-keyman
provides. keyman-config can then depend on this virtual package.
This allows to use fcitx instead of ibus if the fcitx-keyman package
provides that virtual package as well.
