Include open discussion in profile page

[NinaHerrmann]

related to #91
I thought this would be hard, however does not look really hard:

Goal: Include Moodleoverflow discussions started and ongoing Moodleoverflows in profile page

To Implement:

• magic function moodleoverflow_myprofile_navigation to add an item to the user page - this function takes a core_user\output\myprofile\tree argument. Example can be seen in mod_jitsi. However not create a separate block but include below of form entries
• create a overview page, summarizing all courses which have moodleoverflows