Added support for preserving Cartesian coordinates.
Added a new node property, 'shape', that allows to draw square nodes by setting it to 'square'

Added triangle and star shapes.

Added missing semicolons, and filtered for in loops.
Fixed size of square nodes on hover over.
Added safe option to avoid cloning nodes and edges.
Merge branch 'shapes' into development
Merge branch 'Cartesian-Coordinates' into development

Conflicts:
	src/core/graph.js
Merge branch 'development' of https://github.com/timdcrain/sigma.js
Fixed missing brace in plotter.js - now it compiles