added onUpdate() functionality for charts
started to refactor charts
modified Chart to require a JiraClient instance
updated main.js to pass jiraClient instance to charts
add code to load epic in EpicCycleTimeChart
fixed bug displaying report
copied code to draw cycle time chart to EpicCycleTimeChart class
add getTarget() accessor method to Chart
updated EpicCycleTimeChart to do forecasting
added code to filter datasets
fixed/ignored failing tests
Merge pull request #9 from jbrunton/dev-chart-refactor

Refactor charts and add jira filter