Adding Y value unit into linechart popup

- Adding a simplified solution of fetching a meter unit.
- Adding unit into linechart popup, (Rickshaw doesn't support label
  of axis, we may add it in the future, depending on new wireframes).

Fixes bug 1226489

Change-Id: I01aa27578b30e6ad0d27956a3ddd76663f7549ce
Merge "Adding Y value unit into linechart popup"