added shared tooltips to graphs
little fix when searching x index time
fixing the previous fix, now working fine
improved tooltip styles, add multiple highlight points, and changed highligth size when graph plotted without points.
Merge branch 'master' into toni-moreno-add_shared_tooltips_to_graphs
Graph: shared multi series tooltip, refactoring PR #850
Updated changelog with merged PR #850, shared multi series graph tooltip & crosshair
Merge branch 'master' of github.com:grafana/grafana