Drop the use of Qt5 in GeoModelIO

GeoModelIO was part of VP1Light, which uses Qt5 for the GUI. Thus, Qt5 was used for GeoModelIO as well, in particular for containers (QStringLists, QHash, and so forth) and to interface to the SQLite database.

Now, all Qt5 containers have been replaced to their std:: siblings. Plus, the SQLite database is now accessed through the native sqlite3 library, without external wrappers; all the SQL queries have been updated.

While updating the code to remove Qt5, I also improved the code: I implemented DB caches, I removed unnecessary queries and parallelized the code where convenient. The result is a much faster load of the GeoModel data from the database.