Change GUI related command line parameter for Waypoint symbol size into run time...

Change GUI related command line parameter for Waypoint symbol size into run time preference.

Hence command line -s is removed.
Converted 'use small waypoint icons' into (IMHO) a more positive sounding 'use large waypoint icons' in preferences and in function names. Thus reversing the logic in garminsymbols to keep current behaviour and maintain the current defaults.
NB note how the symbol icon index hash must be cleared and then rebuilt when this preference is changed.