Android SDK: Don't pre-install components

During the first round of the Beta phase we observed that:
- people were confused about what was available or not as "preinstalled"
  components
- people tends to explicitly require the pre-installed components in
  order to get latest revisions

By not preinsalling any dependencies on the VM image, each project will
have a more stable .travis.yml configuration (except when Google
introduces breaking changes, like renaming/removing components). It also
simplify the processus to decide whether a component is popular enough
to be preinstalled, or not.
Update changelog (Android SDK updates and fixes)