[themes] tango icons no longer "allowed" in contribs.

[Bèr Kessels]

Hello fellow developers and themers.

First of all, I hope we can all hold our breath, and fingers and not start 
another thread out of this. You might not agree, but leave that for other 
times and places. Thank you ;)

Tango icons use Creative commons (CC) as their licence. 
Whether or not CC is compatible, transformable, integratable or anything else 
is not the point here. 

The result is that you cannot use tango icons in contribs, as was our policy 
for a while. If you have a project using tango (or any CC icons or work, in 
fact) make sure you either replace them with your own work or one of the 
various nice GPL icons around. Make sure you do this an all branches 
(releases). 
If you find modules that still use tango icons, or any other incompatible 
licence, please contact the owner, or leave an issue in the queue for that 
project.

Dries -and the other contrib maintainers- want to keep contribs Pure GPL. This 
is for simpicity. 

« We're not lawyers, so let's try not to  
make up our own rules, or mix licenses without knowing what we are  
doing. » -- Dries

With regards, Bèr