Add plugins.helpers.graph
Add dropNodes and dropEdges
Update Gruntfile
Add renderers.edgeLabels
Update README.md
Update Gruntfile
Refactor utils.getQuadraticControlPoint
Fix https://github.com/Linkurious/sigma.js/issues/2
Fix README
Fix https://github.com/Linkurious/sigma.js/issues/7
Remove hover methods
Fix README
Add helpers for fixed nodes
Merge branch 'master' into HEAD

Conflicts:
	src/utils/sigma.utils.js
Removed duplicated functions from sigma.utils.js

The functions getQuadraticControlPoint, getPointOnQuadraticCurve, getPointOnBezierCurve and getSelfLoopControlPoints were duplicated in sigma.utils.js, due to some weird git merging. I removed the oldest definition.
minor change in settings organization
Merge branch 'master' into merge-pr-381
fine tuning in sigma.settings.js
Related to #263: Restored renderers.def as backup

In d74879... I replaced calling the "def" renderers if not renderer has been found, by using the defaultNodeType / defaultEdgeType for finding the renderer.
Since it caused too much issues with labels renderers, I restored using renderers.def as backup, if no renderer has been found with the node / edge type or the defaultNodeType / defaultEdgeType value.

Later, it will be possible to select which node / edge / label renderer to use from a function, when #368 will be fixed.
Improve plugins.dragNodes