(bootstrap) finished the bootstrap implementation

Still need to finish writing the documentation in doc/Bootstrap.md
NodeServer: support for simultaneous and cumulative connection limits

Limit for number of simultaneous connections is not yet implemented.
BasicNode: added signal emitted on connection close
(bootstrap) Added better error handling on argument-selection failure
live-test: set max-simultaneous-connections to 1 on the server

Reminder: connection-count-limiting for number of _simultaneous_
connections is still unimplemented.