Include "Update Precheck scripts" before LBUpdate do anything

[mschlenstedt]

If exists, call the latest/newest available precheck script before LBUpdate runs rsync. If exit 0, then continue. Anything else will stop the update.

Give options/parameters to the script as the "real" update scripts:

#       release: the final version update is going to (not the version of the script)
#   logfilename: The filename of LoxBerry::Log where the script can append
#   updatedir: The directory where the update resides
#   cron: If 1, the update was triggered automatically by cron```

[mschlenstedt]

Fixed in ba2f3fbbfc003983cf4384762550d489c0ad9e2e