add tests for BoxPlot chart
add charts.utils module for convenience functions and mode polar_to_cartesian there
move charts values convertion to DataAdapter to ChartObject.prepare_values new method
make xgrid and ygrid instance attribute and easier configure (using chained methods)
Merge pull request #1569 from bokeh/task/charts_boxplot_test

add tests for BoxPlot chart
updated tests to include grid refactoring
Don't "fix" singleton array case when expected type is array
fix wrong axis labels being created on Scatter plots with all types of inputs. Now only created for GroupBy objects
fix style comments after PR review first round
fix style comments after PR review second round
Merge pull request #1573 from bokeh/hotfixes/charts

Hotfixes/charts
Merge pull request #1575 from bokeh/mattpap/singleton_array

Don't "fix" singleton array case when expected type is array
Merge branch 'master' into task/1571_deprecations