Easier options to override grid row background colors

[TomTirapani]

GridModel allows devs to set a rowClassFn() to control row-level css classes. Currently, styles set by these row classes can clash with existing styles - for example, changing background-color can break row selection highlight.

Adjust in order to limit unwanted side-effects - ideally, we would be able to set any main style property in a row class and it will behave well with existing styles.