Disentangle properties from algorithms

[jannisborn]

Is your feature request related to a problem? Please describe. Currently, the properties submodule imports stuff from algorithms.core and thus also from that __init__. In the init, we registry all the training pipelines and thus, one needs to have all those dependencies installed, including torchdrug, guacamol_baselines and other vcs-requirements

Describe the solution you'd like Creating a submodule gt4sd.core that specifies base classes used by multiple submodules like gt4sd.algorithms or gt4sd.properties

Describe alternatives you've considered Do the imports only when someone calls list_available_algorithms

NOTE: When creating gt4sd.core we have to make sure that all the rest remains functional, including relative imports, jupyter notebooks (should be fine since we barely import from algorithms.core directly) and in particular also documentation