Update com.koushikdutta.backup/values-gr/strings.xml

Updated the previous string list with the new entries.
I 'll try to find a way to get an alarm specifically on strings.xml change, so I won't get lost in the lot of changes taking place.
Ioannis.
Merge pull request #14 from user024/patch-1

Update com.koushikdutta.backup/values-gr/strings.xml