Enables lists of maps in gremlin

Fixes this issue: https://github.com/neo4j-contrib/gremlin-plugin/issues/7
Update GraphStyle.java to allow custom configuration

By making the constructor public in stead of protected, you can write your own implementations of the NodeStyle and RelationshipStyle interface and create a new GraphStyle with them which you can then pass as a variable in the GraphvizWriter constructor.
Merge pull request #670 from Perfect-Pixel/patch-1

Enables lists of maps in gremlin
Merged in ability to read command files in shell client
Original commit: c7ead9071f2df1c7b3ceecf84eebf27a5b37fbc1
Updates upgrade guide to 1.9 from 1.9.M02
Making it easier to spot the right CREATE syntax.
Merge pull request #722 from PieterJanVanAeken/patch-1

Update GraphStyle.java to allow custom configuration