add log file in source folder

[jedie]

create a log file in source folder with the information about the back runs...

e.g.:

2016-04-26 13:43 backup to \my_backups completed
2016-04-26 13:38 start backup to \my_backups
2016-03-21 11:23 backup to \my_backups completed
2016-03-21 11:18 start backup to \my_backups