Fix branch for installed packages

[juliankuners]

kup loads a list of packages that it manages augmented with information from respectively installed packages . Previously, when a package that is managed by kup is also installed on the users system, the release branch information was lost.

This caused kup install to always install the latest version of the master branch, when the package was already installed. Note: kup update is an alias for kup install. When the release branch of a given package is not the master branch, e.g. for kontrol, then a kup install operation always built the package from source instead of fetching from cache.

The kup list and kup list [package] operations were also broken due to this. In case of kup list, a package was marked as not up-to-date when the respective non-release master branch was installed due to the previously described bug. kup list [package] on the other hand was broken as long as the respective package was installed, as the release branch information got lost, when the package had a release branch different from the master branch.

On another note, the branch that is printed when installing a package without specifically stating a version to install was always master, despite the installed release branch potentially being different.

This pull request fixes the information loss and therefore fixes several bugs/inconsistencies observed with kup install, kup list, and kup list [package]. Also, the branch that is printed now always properly reflects the actual branch that is installed.