first, this fixes#607
also, i think it slightly simplifies code to make "simple" stuff like
names, etc. attributes instead of methods all the time.
so, expect this to be extended to other components, as well.
Now, the error message includes the name of the module that was not
imported, and there's checks to ensure the "more specific" error (i.e. a
failing import *inside* the module) "wins".
Expanding on the implementation in d582016, add a decorator
`core.module.every()` that allows a module to specify how often to
update the module's state.
This can still be overridden using the CLI parameter `interval`.
Add states to the modules and widgets. Widgets are mostly just a
pass-through (backwards compatibility, and ease of use - making states
directly inside the widgets would require more code inside the modules
to ensure that each widget is correctly updated).
Still missing:
- Separators during partial update (right now, it takes one interval
until separators are drawn correctly)
Add a (half-finished) input library, that for now simply allows
registration and triggering of events.
As next steps, the trigger will happen as part of a separate thread that
reads input events.
Additionally, invoking commands via a execute() will be supported.
Thirdly, there is need of a way to selectively update the affected
modules (widgets), which should be possible given that the event
contains both the instance (widget ID) and name (module name).
Parse '-p' parameters and make them accessible via 'parameter()' from
within a module (basically, restore the previous configuration
facility).
Still TODO: Add support for configuration files.
Add logic for parsing commandline options, and a preliminary stub for
loading modules.
Note: The idea is that core.module.load() will return a valid, but
empty, module that displays an error, if the module cannot be loaded
