open_app first sets all the correct paths to the QGIS Python
binary, and secondly opens a QGIS application while importing the most
common Python modules.
Usage
open_app(qgis_env = set_env())
Arguments
qgis_env
Environment settings containing all the paths to run the QGIS
API. For more information, refer to set_env(). Basically, the function
defines a few new environment variables which should not interfere with
other settings.
Value
The function enables a 'tunnel' to the Python QGIS API.