[Android, Bug] Importing not set to fail on invalid

When importing a configuration, Ampersand should explore the file and check to see if its valid. Currently, you are able to select any file type and import it, including images or random binary files. Ampersand should be able to filter the file types, and also check to see if the current selected file is valid. Without seeing if its valid, Ampersand currently perpetually loads without any indication to the user that something is wrong. ### Resources - https://stackoverflow.com/questions/15018308/how-to-restrict-a-user-to-pick-only-jpg-images-from-the-gallery - https://developer.android.com/training/data-storage/shared/documents-files