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
Make the format string of the datetime module configurable using the new
parameter() method in the module.
Also, restructured the setting of the config information a bit so that
the parameter() method can be used in the constructor of a module.
see #23
Until now, widgets were re-created during each iteration. For multiple,
reasons, using static widget objects is much easier, so instead of
creating new widgets continuously, modules now create the widgets during
instantiation and get the list of widgets passed as parameter whenever
an update occurs. During the update, they can still manipulate the
widget list by removing and adding elements as needed.
Advantages:
* Less memory fragmentation (fewer (de)allocations)
* Easier event management (widgets now have static IDs)
* Easier module code (widget contents can simply be the result of a
callback)
see #23
