Fix examples for leaflet 1.x

[elesdoar]

TODO

• [x] ~~Check markers images not found.~~ PR #299
• [x] ~~Mapbox layers in examples~~

Examples to be fixed:

Basic

• [x] ~~108 - Changing tiles~~
• [x] ~~121 - Toggle between two maps on screen~~

Layers

• [x] ~~204 - Dynamic addition/removal of layers~~
• [x] ~~210 - HeatMap WebGL overlay example~~
• [x] ~~220 - Load a map in non standard projection~~
• [ ] 228 - Esri ArcGIS Clustered Layer
• [ ] 229 - Esri ArcGIS Heatmap Layer
• [ ] 230 - Yandex layer example
• [ ] 230 - Mapbox GL Example

Paths

• [x] ~~305 - Path change in group layer (MapQuest)~~

Controls

• [ ] 400 - Dynamic addition and deletion of Overlays control

Mixed

• [ ] 600 - Image Legend Service