Add prestart/poststart/prestop/poststop settings

[nxtn]

Contributes to #256
Fixes #404

<service>
  <prestart>
    <executable>{prestartExecutable}</executable>
    <arguments>{prestartArguments}</arguments>
  </prestart>
  <poststart>
    <executable>{poststartExecutable}</executable>
    <arguments>{poststartArguments}</arguments>
  </poststart>
  <prestop>
    <executable>{prestopExecutable}</executable>
    <arguments>{prestopArguments}</arguments>
  </prestop>
  <poststop>
    <executable>{poststopExecutable}</executable>
    <arguments>{poststopArguments}</arguments>
  </poststop>
</service>