Show xyz options always enabled

Show last placement/farm hints/projected score menubar options are
always enabled, but are not always in sync with what is in the
gamePanel.

Problems:
1. when the options are changed just after startup, before a game is
created, NullPointerExceptions occur, but the menuItem is flagged as
enabled.
2. on Game start, none of the selected options is actually enabled.
variable shadowing

FarmHintsLayer declares a private variable 'visible' while it's parent
class already has a protected variable 'visible'.
Merge pull request #82 from fatsu/ShowOptionsAvailability

Show 'last placement/farm hints/projected' availability