Allow users to cancel each import/export.

- add cancel capability for vCard export.
- use jobId for Notification id, so that users can cancel each
  vCard import/export request.

Note:
As for Notification id, it may conflict with each other when
VCardService is shutdown.

Minor changes:
- add file name to each notification: users can see "xxx.vcf
  is successfully imported" instead of "vcard is successfully
  imported"
- rename mCancelled to mCanceled. strings.xml has "canceled",
  so inconsistent inside the app. Ignore the inconsistency
  between the spell in the app and Future#isCancelled().

Bug: 3215008
Change-Id: I7532e3d1b35a8bbeb694e47077554e36190482ed
13 files changed