[sugar] not use set_tile() in python activities anymore

[Simon Schamijer]

Hi,

After the nearly finished work for trial-3 we like to ask the python 
based activities to not use the self.set_title() method anymore since 
this overwrites the title of the activity window.

The title is set by the base activity class. This allows setting the 
title from the datastore object when resuming from the journal for 
example. The title can be set by the user (in the journal or in the 
activity toolbar).

This change would display the title consistent in the journal, the 
activity toolbar and the palette of the activity in the donut.

More about this issue: https://dev.laptop.org/ticket/3061

We need this to work for FRS.

Best,
   Simon