Facilitate subclasses of SingleTypeAdapter that wish to implement android.widget.Filterable

[jondwillis]

This exposes a new method, getItems() as protected.
Primarily, this allows subclasses to implement android.widget.Filterable more cleanly. The subclass can cache a list of all items. Please let me know if I'm missing something and there's a better way to do this.

I didn't apply this change to any other adapters.

[kevinsawicki]

Looks like the commit currently doesn't compile since imports need to be added for List and Arrays.

I'm totally on board with adding this though.

[jondwillis]

I updated the pull request with the missing imports - that is what I get for editing it using GitHub's interface. I'm not sure how performant getItems() is right now, but it seems to be fine in my limited usage.

It also appears as though your Travis build script is missing ANDROID_HOME.

[kevinsawicki]

Thanks, I've merged this into master.