Gpredict has two configuration layers.

1. A global configuration layer accessible via Edit->Preferences, which applies
   to the whole program.

2. A local configuration layer for modules accessible via the "Settings" button
   in the module configuration dialog.

The global configuration layer is implemented in the sat-pref modules and is
intended to provide useful parameters that can be used as default values. The
local layer is implemented in the mod-cfg module and is intended to allow users
to configure each module individually. If a module does not have its own
configuration the parameters will fall back to their corresponding default
values.

When creating a new module, the module should first try to read the local
configuration parameter using the .mod file and the keys defined in config-keys.h
If a parameter does not exist the modules should read the value from sat-cfg,
which always will return a useful value, i.e. sat-cfg has built-in defaults.
The mod-cfg-util module provides utility functions to warp all this code into
ine single function call for all kinds of used parameters (bool, int, char). The
required parameters for these functions are the local GKeyFile, the local section
definition from config-keys, the key definition from config-keys and the
 parameter definition from sat-cfg.
