DownloadProvider: add to support pause/resume download by manual

This feature contains below points:
1. add to pause running download by manual.
2. add to resume manuallly paused download by manual.
3. add to show proper contents in notification and download-list
   for manually paused status.
4. add to support download breakpoint continuing when HTTP server
   doesn't contain etag in response header. Android baseline only
   supports this when etag is not null.
5. add to show proper contents in notification and download-list
   for status of waiting-for-network.

Change-Id: I433cdee2de8b3add0248bbb0a9d02f8da4e5bb38

Conflicts:
	res/values-zh-rCN/cm_strings.xml
	res/values/slim_strings.xml
	src/com/android/providers/downloads/DownloadNotifier.java