Add timestamp + model number to backup file name

[pstein]

Since I use Holo backup for a couple of Smartphones I would prefer if Holo Backup could add some more unique identification patters to the created backup file name like timestamp and model label and a reference to "Holo backup".

Alltogether the backup file name should look like

holobackup-XT1032-20151123-1528.ab

Could you add this to the next release?

Thank you Peter