CB-6546 android: Add support for allowEdit Camera option

GitHub: Close #12
CB-6546 android: Fix a couple bugs with allowEdit pull request

- Don't set width/height when they are not specified
- photolibrary returns null from getData when image is cropped
CB-6491 add CONTRIBUTING.md
CB-6576 - Returns a specific error message when app has no access to library.

Signed-off-by: Shazron Abdullah <shazron@apache.org>