Added headerCellClassName() and bodyCellClassName() a la rowClassName()

[ironosity]

Added new properties headerCellClassName and bodyCellClassName that are functions which allow a class name to be computed on each body cell or header cell individually. This follows the same pattern as rowClassName() and allows end user to have even greater control over the styling of the table when needed.

[coveralls]

Coverage increased (+0.3%) to 86.452% when pulling 5afde22 on ironosity:master into c537534 on react-component:master.

[ironosity]

If there's anything else I need to do here @yesmeck, just let me know. Thanks!

[yesmeck]

Hi @ironosity, sorry for delayed response, my concern is that Table has too many props. For headerCellClassName, you can use column[className], then query header cell by th.columnClassName. For bodyCellClassName, you can use column[className] with rowClassName, then query body cell by .rowClassName .columnClassName. So I don't think headerCellClassName() and bodyCellClassName() are necessary, less is more.

[ironosity]

Ok, going to close it then. Thank!