Add cloud storage support

[likeadragonmaid]

Add support for the following features:

• Selecting images from cloud storage services.
• Uploading PDF(and other file formats) natively from this app to cloud storage services.

Cloud Services that can be supported:

• Google Drive
• MEGA
• OneDrive (SkyDrive)
• Dropbox
• Box
• Amazon Cloud Drive
• GMX
• MediaFire
• pCloud
• SugarSync
• ownCloud
• Flickr

Resources: https://developers.google.com/drive/api/v3/downloads https://docs.mega.nz/sdk/doc/api.html https://developer.microsoft.com/en-us/onedrive https://www.dropbox.com/developers https://developer.box.com/ https://developer.amazon.com/docs/amazon-drive/ad-sdk-android.html https://www.mediafire.com/developers/ https://docs.pcloud.com/sdks/java.html https://www.sugarsync.com/dev/using-api.html https://doc.owncloud.org/ https://www.flickr.com/services/api/ https://code.google.com/archive/p/flickrj-android/ https://github.com/boncey/Flickr4Javaes/CloudStorage;serviceIds=Dropbox;platformId=Android

[Swati4star]

Is there any library or service which can provide this support?

[likeadragonmaid]

I updated the issue.

[Swati4star]

This issue is too big to be solved at once, I'll break it into simpler issues (one cloud storage at a time) to simplify the development process & reviewing.

[likeadragonmaid]

Any update on "under-review" tag?

[lgoloh]

Hi! Could I add these features for Google Drive?

[Swati4star]

Sure @lgoloh 👍

[vyankatesh24]

@lgoloh Are you still working on it?

[jddeep]

@Swati4star I would like to work on it. But before that please review #645

[jddeep]

@Swati4star I am working on this issue first and then will go back to #132 . As I need more understanding with Android unit testing. Hope you understand.