FEATURE: add support for remote node configuration

- any munin-node could support remote or indirect fetching of plugin's data
- add support for munin-node:remote-node syntax of host parameter
- add process logic to ask for remote node data
- displayname should be used to correctly identify such metrics
FEATURE: multithreaded approach to gather metrics from multiple nodes

- preparation for thread model
 - read configuration for munin-node hosts from file
 - construction of configuration for each thread done
- thread aware signal handler
- syslog logging instead basic one