Allow prefixing gearsloth german job names

[amv]

In order to run the system in gearman servers where one (or all) of the job names gearsloth exposes is already taken by an another server, it would be nice to be able to give a global configuration option which would prefix all of the work names with the given string.

An intermediate fix for this would be to prefix all the gearman job names with "gearsloth_". The configuration option could then be jsut to change "gearsloth" from the prefix to a user specified string.