Control random seed passing to GGB and numerical grades

[TWINGSISTER]

This implementation is somehow messy, all the debug instrumented code is there (although commented out).

Randomness seems to work! When passing different seeds different exercises comes out. This is useful because some GGB activities handle randomness internally and are designed to propose a slightly different activity upon upload. See this example

It is possible to self grade using the numerical variable "grade". In my code it is the default. Boolean variables can be added in the question configuration form.

Think this describes clearly what I have in mind. The application scenario that makes all this meaningful is quite obvious.
I have to reuse wonderful GGB activities. The STAC plugin supported them well!. Still GGB activites tend to guide the student in a path that ends up in an evaluation. When you review such an activity you only get the last GGB screenshot not all the path. Difficult to explain and justify bad marks! When the GGB activity is made up of 10 slightly similar exercises (e.g. 10 (ak+bh)^2) it is far better to do some editing on the GGB code and create a single shot GGB activity (i.e.ONE (ak+bh)^2) and let the repetitions to be handled tracked and reported by this plugin.

[TWINGSISTER]

Added more code to use a plain URL to load the GGB and added an option to put an URL to a version of GGB you are hosting on your own. This is useful to host tests over a LAN or be sure that your tests will run even if something changes in GGB official version.