Legend rasterizer column views

This updates the legend rasterizer with a column view.

Use the following interface:

    /**
     * Add a column to the columnview.
     * @param columnName Name of column.
     * @param explanations {@link Map} of symbols and descriptions inside the column.
     */
    public void addColumn(final String columnName, final Map<String, String> explanations)

    /**
     * Set the columnview title.
     * @param columnViewTitle The title for the columnview.
     */
    public void setColumnViewTitle(final String columnViewTitle)