Browsefield event

Added Player.onBrowseField(self, position) event, it can be useful if we want to cancel browse tiles on certain conditions.

i.e.
```lua
function Player:onBrowseField(position)	
	if position == self:getPosition() then
		self:sendCancelMessage(RETURNVALUE_NOTPOSSIBLE)
		return false
	end
	return true
end
```