Add leaflet recipes sheet about leaflegend

[tomroh]

• use png with addImageLegend
• use symbol with addImageLegend
• makeSymbolIcons Example
• makeSymbolsSize Example
• add overlay groups example
• styling example with title, labelstyle, additional css
• make your own symbol example
• addSymbols example with color
• addSymbolsSize example without color and color legend
• addLegendNumeric legend horizontal & vertical decreasing
• show class turns off bg
• addLegendQuantile use numberFormat is null
• addLegendBin and change shapes ex
• addLegendFactor show re-ordering with factor usage
• addLegendAwesomeIcon ex and show how to use "text" arg
• addLegendSize ex
• addLegendLine ex