feat: more sources and layers

[josxha]

• [x] public API for sources and layers (not 100% of all properties available)
• [x] web: sources
• [x] web: layers
• [x] android: add sources
• [x] android: add layers
• [x] remove source by id
• [x] remove layer by id
• [x] update example app
• [x] support either url or tiles as source parameter (do someone else)

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