Add leaflet recipes sheet

[tomroh]

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