[expo-sdk][android][ios]Allow image picker to choose only images / videos. (#1525)
[expo-sdk][android][ios]Allow image picker to choose only images / videos. (#1525)

* [android][ios][expo-sdk] Allow to choose what media type to select

* [docs] Info about mediaTypes option

* [expo-sdk][android][ios][docs] MediaTypes as a constant; default to images on native side

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