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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Fix representation of negative values in Y axis
update travis script to avoid "exited with 134"
Merge branch 'travis-fix' into correct-min-values-representation
Merge pull request #1 from skywinder/travis-fix

update travis script to avoid "exited with 134"
Auto-update storryboard from Xcode 6.1 + add refresh graph instantly, when press on segments
Fix wrong presentation of years in code exmple (when you click + stepper years starts from 0) now everything works as expected. + rename arrays, accoding Apple guidelines (variables should start from lowercase letter)
Merge branch 'travis-fix' into improve-Example
resolve merge conflict with #79 (it's a subset of these pull-request)
fix issue #80
Merge branch 'travis-fix' into fix-80
Merge pull request #79 from ben181231/master

Fix several UI bug when displaying data with negative numbers
Merge pull request #83 from skywinder/correct-min-values-representation

Fix representation of negative values in Y axis
Merge pull request #85 from skywinder/improve-Example

Fix wrong presentation of years in code exmple + auto-update graph by clicking on segment controll
Merge pull request #86 from skywinder/fix-80

fix issue #80
Changed behavior of property 'enableXAxisLabel'

- Changed documentation for ‘enableXAxisLabel’
- ‘enableXAxisLabel’ now defaults to YES. This way implementing the
method ‘labelOnXAxisForIndex’ is enough to display the labels.
‘enableXAxisLabel’ becomes an option.