Node/layer distances too big in most vis::Graphs layouts

[jurgenvinju]

Describe the bug

To Reproduce

import IO;
copy(|zip+testdata:///m3/snakes-and-ladders-project-source.zip!/|, |tmp:///snakes-and-ladders|, recursive=true)
import lang::java::m3::Core;
import lang::java::m3::AST;
myModel = createM3FromDirectory(|tmp:///snakes-and-ladders/src|);
import vis::Graphs;

Breadthfirst has a lot of whitespace between the layers:

graph({<x,"implements",y> | <x,y> <- myModel.implements} + {<x,"extends",y> | <x,y> <- myModel.extends}, layoutName=CytoLayoutName::breadthfirst())

Circle has enormous radius compared to the nodes:

graph({<x,"implements",y> | <x,y> <- myModel.implements} + {<x,"extends",y> | <x,y> <- myModel.extends}, layoutName=CytoLayoutName::circle())

Expected behavior

• better use of whitespace in a screen, more space for nodes and labels and less for nothing

Screenshots

[jurgenvinju]

• Changed the \layoutName parameter to \layout to provide an entire layout with all of its options.
• \defaultLayoutName is the scheme to get a default layout, like: defaultCircleLayout() and defaultCoseLayout()
• pass in extra options according to each layout's option:

For example, spacingFactor is an option to both circleLayout and breadthfirstLayout:

graph({<x,"implements",y> | <x,y> <- myModel.implements} + {<x,"extends",y> | <x,y> <- myModel.extends}, \layout=defaultCircleLayout(spacingFactor=.5))

graph({<x,"implements",y> | <x,y> <- myModel.implements} + {<x,"extends",y> | <x,y> <- myModel.extends}, \layout=defaultBreadthfirstLayout(spacingFactor=.8))