Android: Allow rotation of canvas activity

[gujjwal00]

This PR enables rotations of VncCanvasActivity with custom configuration handling.

In addition to orientation we also needs to handle screenSize & screenLayout to avoid restart.
Reference: https://developer.android.com/guide/topics/manifest/activity-element.html#config

Depends on: #47 , #48

We can handle the case of activity being killed in background after #46.

[bk138]

Thanks for the PR! What Activity kill are you referring to? Seems pretty stable with this commit...

[gujjwal00]

Canvas activity can killed by the OS when it is in background. Ex:

1. User connects to VNC server.
2. While using the app, user receives a call.
3. Now canvas activity is in background and Android can kill it to free memory.
4. User finishes the call and navigates back to our app.

Step 2 can be anything that pushes our app to background. If we don't keep the connection alive we have to start everything again in step 4. And if user didn't save the password we have to prompt again.

PS:
VNCConn refactoring is nearly finished. I will submit a PR and you can take a look at it.