Support live reload of configuration

[andygrunwald]

Configs should be reloadable by some kind of unix signal or by socket communication (mini protocol).
The modification part should be done by calling Configure() again. Plugins will have to react accordingly.

Server part:

• Password protected (provided via command line parameter, SHA512 encoded)
• Add plugin: id + config
• Remove plugin: id
• Modify plugin config: id + config
• Reset all (like signal part)

Signal part:

• Use any not-yet-used signal like SIGUSR
• Create a diff between current state and config loaded
• Add new plugins
• Reconfigure existing plugins
• Remove all plugins not existing in new config
• Start new producers
• Start new consumers

Important: This is just an idea and this ticket can be used for a discussion. You have ideas? Feel free to add them here. You have concerns? Add a comment! Or maybe you have an idea how to develop it? Feel free to run a prototype.

For this feature, the architecture change that is coming in v0.5 is required.