Move injected code from typesystems

I went through the typesystem XML files and extract
the code inside "inject-code" tags which is not
stored on templates, and put them on a main directory
called glue on the top of the modules sources.

Having all these pieces of code on cpp files allows us
to not have to modifying C++ code inside XML files,
which is quite tedious considering that one need to escape
some symbols.

The following typesystems were reviewed:

• QtCore
• QtGui
• QtWidgets

Besides looking into the typesystem of the other modules
we can consider transforming some templates into a separate
file.
We need to take care that in some cases we use templates
modifying their parameters, so I don't know if that is
possible having the source of the template on a separate
cpp file.

Pending tasks:

• Review missing modules
• Analyze how convenient it's to extract some static templates too