Replace specific item types with generic DataItem

Using a generic DataItem allows to re-use the same data for different
chart types.

For charts that require two-dimensional data points (like LineChart),
add DataItem2D that adds an x value and use the super type's value as y.

LineChart can also use DataItem, in this case the x value will be the
index.

Change-Id: If0a275424be518778273311d4a1e091569da9141
20 files changed
tree: fa593193d4b51b7ae8337a089db7fd45bf156c61
  1. .gitignore
  2. bundles/
  3. component.xml
  4. examples/
  5. pom.xml
  6. releng/
  7. tests/