testing the single QQmlEngine plasmashell

[Marco Martin]

Hi all,
I've pushed all what's needed for running plasmashell with a single 
QQmlEngine, surprisingly seemed to have taken less work/problems than i 
feared.

the repos are needed are:
* kdeclarative
* plasma-framework
* plasma-workspace
* plasma-desktop

the branch is always called mart/singleQmlEngineExperiment in all repos
last two is due to all applets having added 
X-Plasma-RequiredExtensions=SharedEngine
in the metadata file (still on the fence with an X-Plasma-RequiredAPIVersion 
key instead)

now all applets in a default setup, in p-d and p-w should share one single 
engine (on a normal setup still networkmanager and bluetooth would make their 
own engines) could still need some change in plasmashell and kdeclarative if 
we want to go all the way and reuse the same engine for the desktop/panel 
views as well.

please test it to see if there are obvious regressions, if it's faster or 
slower, more or less crashy, if it takes more or less memory (dere it slims by 
about 25 MB on a 32bit system, of about 40 on a 64 bit), good profiling of 
memory and startup time may be nice as well (will try in massif later)
particularly important to test as many aplets as possible, as it may be 
perfect for one and break another

known regression atm is broken translations but should be easily fixable

-- 
Marco Martin