Allow building against system packages
Currently, the app includes several
git submodules, which are strictly required to build it. However, there is no way to build against system versions of the appropriate libraries. This makes integration e.g. into Linux distributions difficult. For example, distributions like Fedora mandate, that if there is a system version of a particular library, that one must be used.
To enable this, we should allow building the app against system versions of all libraries. This can be limited to the
cmake build (as this is what we will migrate towards).