midi_action.h
midi_action.cpp

Added
-a "QString parameter3" to MidiAction (with getter and setter)
-the new MidiAction "SELECT_NEXT_PATTERN_CATEGORY"
The latter uses parameter3 to switch patterns within a category.

preferences.cpp:
-Along with the MidiActions parameter3 is saved in the preferences.
-removed duplicated code in loadPreferences

So far parameter3 is not visible or settable in the GUI (midiTable).