Save dialog support ?

[meypod]

Feature
In cases we have file path, this works great, but when we want to let the user save a file where they want, we have to jump to the native side to do the save requests/dialogs

Motivation
while react-native-document-picker works great for picking files to get the path and use this package to read the content, we don't have a way to write anything back to fs with control given to user, usually as a save dialiog/file picker

Details
I think both file picking for opening and file picking for saving, and writing to and reading from them, needs to be inside a single package, it makes more sense and potentially reuses some code