Added function to query the tile database and functions to do calculations on a quadkey

Karsten Prehn requested to merge feature/pre-calculations into main

This MR adds a function to connect to the tile database for different purposes (reading, writing single and writing multiple entries), a function that reads from the tile database the contents that fall in a bounding box and a function that transforms a lower level quadkey into an all L18 grid representation. Additionally some helper functions are added.

\approve @marius @ds

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