Zabbix settings backup, Readme update, base calls location move

New module for zabbix settings backup based on zabbix-dump

Move the _BORG_CALL and _BORG_PRUNE base calls to functions.check
instead of each module (they are all the same)

Update Readme file

Update default settings and remove KEEP so the original defaults are
used

borg.backup.settings-default

@@ -34,7 +34,7 @@ FORCE_CHECK="";
 # it can also be "{hostname}-{user}-{now:%Y-%m-%dT%H:%M:%S.%f}"
 BACKUP_SET="";
 # prune times, how many are kept in each time frame
-KEEP_DAYS=7;
-KEEP_WEEKS=4;
-KEEP_MONTHS=6;
-KEEP_YEARS=1;
+KEEP_DAYS="";
+KEEP_WEEKS="";
+KEEP_MONTHS="";
+KEEP_YEARS="";