First go at syntax to display similar pages

First go at syntax to display similar pages

added helper to quickly check the available models

show similarity scores in CLI

refactoring to make models selectable

This makes it much easier to add new models. Models can now be selected
via the configuration

added usage statistics

add index clearing, cleanup

fix access of sources

firs go at abrstracting the storage backend and using sqlite

Requires the dev branch of the sqlite plugin

added info method for kd tree inspection

More robustness in creating the index

Retry failed API connections, do not abort the whole indexing and rather
skip a chunk. CLI testing tool for the split mechanism

fix logging in CLI mode

some more doc blocks

Frontend integration with simple syntax component

support chatting

asking standalone question works

initial checkin. working vector storage and similarity search