Revert VisualizationView

[dwlee]

• Revert addLayer from hydro version
• Delete layer NullChecker in onCreate

https://github.com/robotics-in-concert/android_core/pull/1#issuecomment-87159668

[stonier]

@dwlee The 'why' is always useful with the 'what' for fundamental changes like these ;)

Github issues are better than people's memories.

For the record, this is to cope with the hydro-indigo changes to move most things with the visualisation view into the onCreate function instead of the init function. This however, doesn't let us handle setting of topic names via the nameresolver which can only be called from the init function where a node handle is available. We use this to configure remappings for the various layers.

Two ways to handle this: 1) delaying the addLayer or 2) allowing configuration setters for topic names that can be called before the visualisation view's init function (which in turn calls all the layer's init functions).

We went for 1) here as it only requires minimal touching of android core. 2) might be better to provide a consistent approach whereby layers are always provisionally setup in onCreate but would require a hacking on all layers.