Enable widget sensitivity in the layer properties to be controlled.

Enable widget sensitivity in the layer properties to be controlled.

Some settings are only relevant when other settings are in the right state.

Allow control of the sensitivities to be adjusted when changes to the widget values have been made.
Changes to each widget have to be considered separately (referenced via the parameter enumeration numbers).

Also expose the label widgets so they many be controlled.

ATM control these settings:
Maps:
 Auto Download -> Auto Download Only Missing
TrackWaypoints:
 Waypoint Draw Labels -> Font Size, Colour, BG Colour & BG Translucency.
 Waypoint Draw Image -> Image Size, Image Alpha + Cache Size.
 Track Draw Mode -> All Tracks Colour

NB Since most track settings have been split across into the Advanced tab,
 IMHO controlling sensitivities of widgets in another tab is not obvious,
 so these relationships have not been changed.