battery_dash_widget: Tooltip states name of battery.
battery_dash_widget: float values are rounded.
Merge pull request #21 from dornhege/groovy-devel

I confirmed that the proposed part (to avoid float value rounded) works, by unit test file I'll upload later.

I haven't been able to test With real robots -- I only have an access to `PR2`, of which dashboard overrides `BatteryDashWidget`.`update_time` method.