QtExtraControls -> KQuickControlsAddons

[Marco Martin]

Hi all,
I have a proposal of renaming the QtExtraControls import to 
KQuickControlsAddons.
the rationale is the review Kevin gave for having it in frameworks, and using 
the Qt prefix is in general not a good idea (and prone to future collisions)

the downside is that every plasmoid has to be converted but is perl-able. If 
it's done, should be done asap

-- 
Marco Martin