[birt-dev] CheckIn: Difference chart renderer 2D implementation

["Yulin Wang" <yulin.wang@xxxxxxxxxxx>]

- Summary:
Difference chart renderer 2D implementation

- Bugzilla Bug (s) Resolved:


- Description:
Added Fill render for polygon and curve line.
Refactored code and updated Line render for polygon and curve line.

- Tests Description: Manual test
- Notes to Build Team: None
- Notes to Developers: None
- Notes to QA: None
- Notes to Documentation: None

- Files Edited:
/org.eclipse.birt.chart.engine.extension/src/org/eclipse/birt/chart/render/Difference.java
/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/render/CurveRenderer.java
/org.eclipse.birt.chart.examples/src/org/eclipse/birt/chart/examples/api/viewer/PrimitiveCharts.java
/org.eclipse.birt.chart.examples/src/org/eclipse/birt/chart/examples/api/viewer/SwingChartViewerSelector.java

- Files Added:
/org.eclipse.birt.chart.engine.extension/src/org/eclipse/birt/chart/render/DifferenceRenderer.java

- Files Deleted