gaTooltip can be enabled and disabled programmatically.
Added Functions enableTooltip and disableTooltip to ga.Map.
Added property enabled to ga.Tooltip.
Adden Functiond enable and disable to ga.Tooltip.
Changes to be consistent with existing coding style.
Added @api annotation to public functions of ga.Map.
Merge pull request #99 from DKPillo/dev_dynamic_tooltip

gaTooltip can be enabled and disabled programmatically.