Add restrictions to invalid chart data

[yileifeng]

Description

Will be one of the last tasks and a substantial one: need a robust solution to handling all cases of invalid data input. Should consider the following and more:

• invalid CSV cell values (should be numeric or a percentage value outside of the first column which can be categories for certain chart types)
• valid data for each chart type (e.g. pie chart should be formatted as first column of categories and second column representing percentages of the pie)
• some type of JSON validation when importing an existing Highcharts configuration

There will probably be an extensive list of edge cases especially with hybrid chart types. Requires much testing.