implement on-demand creation of widget() for kdevelop

this unbreaks katepart again for any apps using multiple views
like kwrite/kate

while this breakage was more a accident by a commit of a kdevelop dev
to fix their probs, which is not bad, mattr has shown again, that cooperation
with kdevelop devs is just close to zero, as neither they care to
tell kate devs in advance what they need or which probs they have but more
like to commit fixes which cause probs for any other app than kdevelop...

But yeah, mattr has explained it to me, why cate, it will only break kate....
perfect logical ;)

for future: next time ask for changes, if you don't know how to make them correct without breaking other people code just to avoid to have 2 more qobject_casts in your own code. if nobody on kwrite-devel reacts for reasonable timeframe, you still can
kill the stuff on your own...

it's pure fun to implement features for people not even respecting at all that there are even people maintaining katepart, don't think they would like that other people do the same in kdevelop's code, but sure, why take the same care on the code of other people :)

btw., the kate devs even created a ktexteditor-devel mailinglist for that purpose and on request
of kdevelop guys like mattr, nice to see that it is used that well............

have fun with the feature, hope it works, if not, please report on kwrite-devel or fix it if you are sure you know how....