CMUpdater: Create DownloadNotifier, simplify DownloadReceiver logic.

Change-Id: I5bddddead4f87f040278a9fe1381a5a5ad2df95b
CMUpdater: Handle download complete in background thread.

  - Since a broadcast receiver's timeout is ~10s, we should avoid doing
  too many operations, and instead offload to an intentservice.

Change-Id: I713acfd078e3e81ed7405e027259429e7c3481ae
CMUpdater: Create builder for UpdateInfo. Simplify codebase.

Change-Id: I9e6f3d0eda8fc2cd45d5009f0ec915b8e3f9d8be
CMUpdater: Switch all network requests to utilize Volley.

Change-Id: I9ef137f9fbd6196564235306109eaf77c58f81ac
CMUpdater: Fetch changelogs for updates only if explicitly requested.

Change-Id: I7ba3a8436e7de3d6484bc81e751af204860d9969
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_packages_apps_CMUpdater.git into 'cm-11.0'