chore(ios,v10): various fixes, warn if below/aboveLayerID doesn't exi…

[mfazekas]

…sts.

Deprecations:

• Using images directly in styles is not deprecated. Use the images component instead. image-in-style-deprecated
• When a source/layer refers to an existing on in the style you should use the existing attribute. source-layers-existing

Other changes:

• Some refactoring/swift bang fixes
• Allow other components not only layers hosted in Source component (example is Images)
• Source no longer waits for styleLoaded. This prevented adding a Source and Layer referring that with sourceID, as Layers were attempted to be loaded immediately, while Sources were waiting for load of style.
• HeadingIndicator now uses Image component instead of iconImage: require(..) so we can deprecate that. Also heading indicator now sepcifies the sourceID directly.