major overhauls in plasma declarative for dataengines

[Aaron J. Seigo]

hi all...

last night i committed to master in kde-runtime some major changes to the code 
that handles the briding of Plasma::DataEngine into QML. there was some 
complexity in there that was unnecessary and some performance improvements to 
be found as well.

there is still an issue with performance left that i'm not 100% sure yet how 
to deal with: DataSource keeps a local copy of all Plasma::DataEngine::Data 
... which means that when the Data changes, it will cause a bunch of 
allocations as data members get detached, which then gets all thrown away 
instantly when dataUpdated gets called.

in any case, i'm not comfortable backporting this to the KDE/4.7 branch right 
now. it's functionally equivalent to the old code, so no majorly disruptive 
changes (Marco: i ended up putting the source filter back in), but it needs 
more testing.

if you are using kde-runtime from master with QML, please try to keep an eye 
out for any anomolies related to dataengines.

everything is working perfectly here, but i may have missed something.

-- 
Aaron J. Seigo
humru othro a kohnu se
GPG Fingerprint: 8B8B 2209 0C6F 7C47 B1EA  EE75 D6B7 2EB1 A7F1 DB43

KDE core developer sponsored by Qt Development Frameworks
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