FileResponseHandler: handleResponse(): Simplify the code.

Use HttpEntity.writeTo() instead of looping ourselves.
ItemsContentProvider: Move simple HTTP downloading into HttpUtils.
FileResponseHandler: Optionally decompress gzipped content.

Unfortunately we cannot now use writeTo() to simplify the code.
Child-fragments layout: Remove extra padding.

The parent fragment already has padding around its edges.
Classify fragment layout: Use just one top-level ScrollView.

Instead of a separate ScrollView in each child fragment.
DecisionTree: Avoid some duplication of code.
Remove a now-unnecessary comment.
Singleton: Add, and use, an init() method with a callback.

We can then do the initialization in an AsyncTask.
ClassifyFragment: Add and use showLoadingView helper method.
Fix some comments.
Singleton.init(): Do the initialization in an AsyncTask.
Get, and show, the icons for the answers and checkboxes.

This get the single .png file containing all the icons,
and then parses (hackily, not robustly) the CSS (without a stable URI)
to get the positions of each icon in the file, then splits it up.

The cache is not yet preserved across sessions.