Add cube support.

[gbrlsnts]

By adding cube support we can view very high quality 360 scenarios since OpenGL has a max texture limit. Using one bitmap this texture must be used for all of the 360 while with a cube this limit is applied for each face of the cube. In the example I included you have 2048x2048 faces.

The demo I just copied your examples and added cubemap, so it might be a bit clunky though I just wanted to get the demo up and running.

To use the cubemap you need to set the projection mode to CUBE and use asCubemap like you do for asBitmap and asVideo.

To load each face, onProvideCubemap is executed for each face to be loaded. After all faces loaded onReady is called.

With the example I used Picasso as you already have. In my project I used Glide. Inside onReady in the demo, I called cancelBusy and in my project I use that to hide the overlay on top to hide the loading process and display loading spinners like you do. This allows very good flexibility.

I'm not sure to which branch to push, so I created the request for master.

[ashqal]

Awesome! I will check it ASAP.

[ashqal]

Thanks for your quality PR.

[gbrlsnts]

Thank you. If you need any change let me know. I will also try to add a minor stuff I have done as well.