The old approach of using a local checkout does not work anymore
after the Git migration. One could use
`pkgctl repo clone --universe` to get a similar checkout but this
takes ages on my server. So let's better just download the
individual sources as needed, similar to how it is done for AUR
packages.
* Break backwards compatibility
* Allow to deserialize only base-data of packages and build
actions to potentially speed up showing tables
* Speed up package search in many cases by only deserializing
base-data (unless details are actually wanted)
Martchus