Start a picker to choose image if no image uri is provided

[adwiv]

There is no change in the way library is invoked, except that it now allows you to pass a null or empty Uri.

The changes in this PR are:

CropImage

• CropImage.activity(Uri) method does not throw exception if image uri is null or empty. We can also alternatively create a new method, but I thought this might be better to have a single entry point.
• If camera permission is not available when collect the intents to show the image pickers, the camera related intents are ignored. This allows us to create a picker without always needing the camera permission.
• Changes to annotations for allowing null uri and remove lint warnings.

CropImageActivity

• If the passed uri requires storage permission, request the permission and set image after receiving permission.
• If the passed uri is null, start a picker. However, if camera permission is explicitly required, request the camera permission first and then start the picker in the onRequestPermissionsResult.
• We dont care whether the user allowed or denied the camera permission. CropImage picker will automatically remove the camera intents if permission is not available.

AndroidManifest of QuickStart Sample

• Request Camera permission to test for permission handling. Not actually required for quickstart sample. Can be removed after testing.

QuickStart MainActivity

• Removed unnecessary code not required after the new change.

[ArthurHub]

Sorry it took me so long to check your PR.

AWESOME WORK! LOVE IT!