Updated all chart types to use the helper.getHoverColor. Pattern fills can now be specified for both fill and line portions of a chart. Updates chartjs/Chart.js#1323
Meta info are now scoped by chart and moved under the dataset._meta map { chart.id -> meta }. Meta for a specific chart (and dataset) can be accessed using chart.getDatasetMeta(datasetIndex) or from the dataset controller using getMeta(). Note that helpers.uid() now generates an int (instead of a string) to make lookups in the _meta map faster.
