[Kst] kst2 datasource API comments

[Peter Kümmel]

Barth Netterfield wrote:
>>  are lots of small functions which I'm wondering about. It would at least
>>  be good to have somewhere a clear list of the minimum to implement when
>>  creating a new datasource, to avoid overwhelming potential new
>>  contributors. Examples include init() vs initPlugins(), cleanupForExit()
>>  vs the destructor, findOrLoadSource() vs loadSource(), validSource() vs
>>  isValid(), configWidgetForSource() vs configWidgetForPlugin() vs
>>  configWidget(), save() vs saveSource(), etc... 
> 
> This all needs cleanup.  I also don't know what is going on there.  However, 
> there is a demo data source which can be filled in pretty easily.  However, 
> most of the things you mention don't need to be re-implemented in the data 
> source.  Documentation in the header should be improved.

For a demo sampledatasource.cpp is a little bit too big I think.

Peter