Fix several UI bug when displaying data with negative numbers

- Fix the method calculating max value of the data
- Fix the Y Axis Label Offset when displaying nagative numbers
- Fix the Pop Up Report when displaying nagative numbers
Add enable X-axis flag
Add customization on graph padding
Add delegate method to control visibility of the "No Data" label
Updated draw dots method for performance

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update travis script to avoid "exited with 134"
Merge pull request #1 from skywinder/travis-fix

update travis script to avoid "exited with 134"
Merge pull request #79 from ben181231/master

Fix several UI bug when displaying data with negative numbers