[Feature Request] Helper interoperability

[hiddeninthesand]

As mentioned over Matrix, Tap adds the field MPR-Package: ${pkgbase} to the deb's control file. This should let Una recognize that there's previously installed MPR packages, in turn Una should also mark installed packages as MPR packages.

• Mark the packages so other helpers can recognize them
• Read marked packages from APT so Una can recognize packages installed by other helpers

[RudraSwat]

I've added the MPR-Package field, as well as an MPR-Version field with the version of the package in the MPR cache (not pkgver) at the time of installation.