Remove the need for ChanMap

[MatthewWhiting]

A more sensible way for Object3D to work is to have a std::map<int,Object2D*> that associates a single Object2D with each z value.

This makes it clear that there is only one Object2D for a given value of z.

It will require the way all the ChanMap stuff is referenced ie. replacing maplist[m] with map[m].second etc. It might make things a bit more efficient as well, since we'll be able to use iterators etc.

[MatthewWhiting]

Added note: this came up from looking at Detection::hasEnoughChannels() and thinking that there should be a way to implement this in the Object3D class. It will be simpler with it set up as a std::map, since the channels will be already ordered and we can just cycle through them counting the maximum number of consecutive channels.

[MatthewWhiting]

Have merged these changes back into the trunk in [570], so will go with it. Have removed ChanMap?.{cc,hh} from the Makefile as well, since we don't need them any more.

Closing the ticket.