Service framework background tasks and watchdogs (#39)

* Service framework background task

 - Implement an optional background task for services that starts automatically on service start.
 - Implement a watchdog that updates the service's status when its task fails at runtime

* WIP: Partially implemented

 - Background task startup + watchdog implemented for service startup
 - Implementation for service shutdown missing
 - Handling of watchdog triggers of essential tasks missing

* Refactor of service framework

Split service framework into multiple submodules

* Implement Watchdog module

* Optimize Watchdog module

Make usage of Watchdog more flexible

* Refactor start_service

Refactor the giant block of cod e into smaller helper methods where possible

* Edit StartupError string representations

* Finish refactor of start_service method

* Refactor stop_service

 - Apply same refactoring to stop_service
 - Increase name placeholder space to 30 in logger

rustfmt.toml

@@ -0,0 +1 @@
+max_width = 110

src/log.rs

@@ -25,7 +25,7 @@ pub fn setup() -> Result<(), SetLoggerError> {
  fern::Dispatch::new()
  .format(move |out, message, record| {
  out.finish(format_args!(
- "[{} {: <25} {: <5}] {}",
+ "[{} {: <30} {: <5}] {}",
  humantime::format_rfc3339_seconds(SystemTime::now()),
  record.target(),
  colors.color(record.level()),