Adds ability to define the minimal edge's arrow size.
add edge quadtree
change maxElements and maxLevels
add edge hover
Merge branch 'edge-quadtree' into events.edges
index only if drawEdges=true
add _enabled to deactivate the quad on demand
deactivate edgequad when FA2 is running
deactivate edgequad on node drag
deactivate edgequad on animation
add nodes highlight on edge hover
update unit tests
fix lint issues
index only if enableEdgeHovering is true
enableEdgeHovering: false by default
fix lint
Merge branch 'master' into merge316

Conflicts:
	src/misc/sigma.misc.bindEvents.js
	src/sigma.core.js

Also ported some modifs from PR #307 to edge events related code (might not fully work yet).
Merge remote-tracking branch 'origin/pr/316' into merge316

Conflicts:
	src/misc/sigma.misc.bindEvents.js
regenerated examples imports
Cleaned a bit sigma.utils.js