AIDA: use sig_something() += / -= syntax to (dis-)connect signal handlers
AIDA: fix signal handler_id into a size_t
AIDA: minor rename
UI: ensure all signal handler connection ids have type size_t
AIDA: add Aida::Connector to provide a (dis-)connect interface on SmartHandles
AIDA: use sig_something() += / -= syntax also for SmartHandles
Merge branch 'unified-signals'

* unified-signals:
  AIDA: use sig_something() += / -= syntax also for SmartHandles
  AIDA: add Aida::Connector to provide a (dis-)connect interface on SmartHandles
  UI: ensure all signal handler connection ids have type size_t
  AIDA: minor rename
  AIDA: fix signal handler_id into a size_t
  AIDA: use sig_something() += / -= syntax to (dis-)connect signal handlers