Feature/optimize multiuser bckrestore

[myroad94]

Modification:

1. backup.sh: Some app can be installed only for some user but not for user 0. This fixes it by list pkg per user.
2. backup.sh: accounts.db is not used anymore in Android 9. accounts_ce.db and accounts_de.db supersedes it. Using tar instead of cp to preserve rights.
3. restore.sh: restore only if it was installed for the user during backup, based on presence on data or .disabled file.

[myroad94]

BTW, thanks to the author for the great work of multi-user backup! The only one that exist so far, AFAIK.

[Beneter]

LGTM