Show RTT measured by ICMP echo request/replies for a given host.
For that to work correctly, change the "full_text" callback for a widget
so that the widget itself is also passed as argument in the callback
method. That actually makes a lot of sense, since the widget can now be
used as a repository of state information.
see #23
Quite a lot of modules use the "if higher X -> critical, if higher Y ->
warning" idiom now, so extracted that into a common function for reuse.
see #23
This is going to be a bit more comprehensive than anticipated. In order
to cleanly refactor the core and the engine, basically start from
scratch with the implementation.
Goals:
* Test coverage
* Maintain backwards compatibility with module interface as much as
possible (but still make modules easier to code)
* Simplicity
see #23
Hide alias concept for modules in the engine. That way, the individual
modules never get to know about whether a module has been aliased or
not.
see #23
