Mac advanced prefs: adapt sting list config control

The mac widgets for module list and string list should be adapted to the qt variant:

string list should use config_GetPszChoices (core.c)
CONFIG_ITEM_MODULE should be a string list and not module config control

Using config_GetPszChoices, entries for "Default" and "deactivate" will be added automatically.

Currently, Default is added manually, and has more or less hacked in the functionality of deactivate. (E.g.: default audio visualiser, default avcodec-hw mechanism)

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