Default to having a unique homology map; make the homology map selector an advanced configurable option

[ihh]

There was some discussion of homology maps (I'm just going to start calling them this, cf #4370) in the Apollo planning meeting today. While I definitely see the use cases for having multiple maps (e.g. #4327), I am generally concerned that for most users this will be a niche use case; they will want synteny to "just work".

I wonder if we should make the homology map a configurable option, disabled by default.

I am framing this as a question rather than a feature request, because I can see it might need further discussion. Also, it is highly relevant to the protocols article on synteny which we are due to start shortly, so I wanted to get it discussed before we begin that.

@cmdcolin @garrettjstevens

[ihh]

Maybe it should be a feature request actually... anyway over to you