SubjectAdder: downloadMissingImages() Fix the build.
SyncAdapter: Avoid multiple simultaneous requests for objects.

Because this would just slow us down and lead to use getting items we don't need
when using a slow connection.
SubjectFragment: Ignore "next" items.

The parent ClassifyFragment will give a real item ID to its child
SubjectFragment anyway, so this would be an unnecessary simultaneous
request for a first item at first startup.
About: Mention the license of the answer icons and example icons.

Because we now bundle them.
About: Change the CC license name for the app icon image.

Because eso.org seems to have changed from
Creative Commons 3.0 Unported
to
Creative Commons Attribution 4.0 International
QuestionFragment: Do not use == to compare Strings.

Sometimes I forget that this is not C++.
strings.xml: Escape ' with \.
build.gradle: Update build-tools and compat versions.
1.16