Searches for the style having the specified levels. Adds if not found (optionally)
function FindStyleWithLevels(Levels: TRVListLevelCollection;
const StyleNameForAdding: String; AddIfNotFound: Boolean): Integer;
This method searches for the style having levels with properties like in Levels.
If AddIfNotFound=True and style is not found, it adds a new style to the end of collection, assigns Levels to its Levels and StyleNameForAdding to its StyleName. The created style has Standard property = False.
Index of style, or -1 if not found (and not added).