* gz: use server config file for loading world plugins
* submodule
* use server.config in tree
* newlines
* format
* gzbridge: rename function
* format
* gzbridge: add magnetometer callback
* change gz_find_package to find_package
* fix up directory structure and cmake to allow multiple plugins
* newlines
* add comment block explaining gz_env.sh
* remove dupe readme
* remove SENS_EN_MAGSIM from all gz airframe files except spacecraft
* update gz submodule
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