[Kbabel] Plugin-based import/export

[Stanislav Visnovsky]

Hi!

I've just commited subj. into HEAD. It means that KBabel now sort of
"supports" multiple formats of files. The source is still very much
PO-centric, but I don't want to change more than necessary. If some plugin
needs changes, they should be made if reasonable - this is unstable branch
and the interface can change.

Dark side: the code is not that well tested, so there can be data loss 
when saving/loading - you have been warned.

I would be happy to hear any comments, flames, bug reports etc.

Have a happy New Year!

Stanislav