Adding Python bindings for some frameworks in the next release

[Stephen Kelly]

Hi,

I would like to add the python bindings previously discussed to the next 
release of KF5.  This means adding the four most recent commits from 

 https://github.com/steveire/extra-cmake-modules/commits/python-bindings

to ECM and generating the bindings for KItemModels and KGuiAddons, 
KDbusAddons. 

I chose these three because they do not require non-default 'rules' files 
for the bindings. Eg:

 https://github.com/steveire/kitemmodels/commit/98bf569340a5a5049711e087429d080708deb7b8

This way we can iron out any distribution related problems in the approach, 
then extend the system to further frameworks.

Unfortunately this can not yet be CI tested:

 https://phabricator.kde.org/T2389

but there are unit tests in the ECM repo for this system.

Any objections?

I would very much welcome review of the ECM code in particular.

Thanks,

Steve.