Bug 582265 - Logout and Learning Path features added

- logout and Hint Request Button added
- logout button added with its related functionality to stop and resume
the game later.
- added the learning path concept. Now each game is a learning path with
a set of learning activity that guides the student to follow a specific
path with different learning activity types on Modeling

Signed-off-by: Antonio <bucchiarone@fbk.eu>
Change-Id: Ia111b27fe6770f587e8b9769654bf6dfc546319e